In a US Stand-Your-Ground state, is it legal to shoot someone who accidentally enters a home?

This varies widely by state

Every state will have very specific statutes about this. This is known as castle doctrine self defense, and pre-dates stand-your-ground laws by decades.

Louisiana Revised Statute RS 14:20 defines justifiable homicide, including:

When committed by a person lawfully inside a dwelling, a place of business, or a motor vehicle as defined in R.S. 32:1(40) when the conflict began, against a person who is attempting to make an unlawful entry into the dwelling, place of business, or motor vehicle, or who has made an unlawful entry into the dwelling, place of business, or motor vehicle, and the person committing the homicide reasonably believes that the use of deadly force is necessary to prevent the entry or to compel the intruder to leave the dwelling, place of business, or motor vehicle.

This is not a blanket permission to kill anyone inside your home, but will be a high bar to prosecute. You're probably not going to be able to shoot someone passed out on your floor, for example. Your example would likely hinge on whether or not the entry was unlawful. The state of mind of the homeowner is typically part of the defense, and of course the homeowner is the one who gets to testify as to their state of mind.

These laws are very specific by state. Some states do not include these defenses by statute at all. I would estimate that all the "stand-your-ground" states will have some form of castle doctrine legislation.

Your question misunderstands the nature of self defense laws in general, with the stand your ground and castle doctrine just being special cases.

In order to claim self defense, you have to assert that you thought there was a danger, and then that assertion is judged as to whether it was “reasonable” or not. This judgement is initially made by the prosecution as professional judgement whether it is true and/or whether they can get a conviction in the face of such an argument. If they don’t believe you or want a trial anyway, then by a jury.

If you watch a 9 month old baby crawl down the sidewalk, and then up into your house through an open door and then take an axe and kill the baby claiming castle doctrine or stand your ground or any other form of self defense, is going to be utterly useless in all 50 states. The prosecution won’t buy it and neither will the jury.

If on the other hand, a 6 foot 8, 300 pound, body building, martial artist, convicted serial killer escapes from prison, and is discovered asleep on the floor of your living room with a gun in one hand and a knife in the other, and you blast him with a shotgun as soon as you identify him, a claim of self defense may be viable depending on your local laws (and the jury)

Having him awake and standing in the center of the room and it’s going to be viable in even more.

Having him awake and advancing on you, even more.

Having him advance on you while saying he’s going to kill you, and it’s probably a slam dunk in every state, with the prosecution not even bothering to put it to the test, even if you tell the cops you are glad he’s dead and he had it coming.

If your hypothetical house cleaner was caught vacuuming the living room floor, keep your mouth shut and hope you have an inventive and convincing attorney, otherwise you’ll probably be convicted of premeditated murder.

I can’t think of a circumstance where it would be reasonable to kill someone while they were doing nothing more than vacuuming the floor without my personal permission.

One last factor in some states is that when a defendant was in their home when they used deadly force against another person, there is a presumption that their belief that the other person was an imminent deadly force threat. For example, Florida 776.013

(2) A person is presumed to have held a reasonable fear of imminent peril of death or great bodily harm to himself or herself or another when using or threatening to use defensive force that is intended or likely to cause death or great bodily harm to another if:

(a) The person against whom the defensive force was used or threatened was in the process of unlawfully and forcefully entering, or had unlawfully and forcibly entered, a dwelling, residence, or occupied vehicle, or if that person had removed or was attempting to remove another against that person’s will from the dwelling, residence, or occupied vehicle; and

Normally the defense has to produce at least a little evidence on each legal requirement of self-defense in order to argue self-defense to a jury. This presumption would relieve the defense of having to present evidence that the victim of the force was a deadly force threat if that person was in the process of forcibly entering the defendant's home. The unlocked door in the hypothetical would present a problem to the defense if they were trying to raise this issue though, since it seems like it wouldn't be reasonable for the defendant to think that the person was forcibly entering their house if the door was unlocked. While there is a presumption, it is rebuttable by the prosecution, who would certainly rebut it at trial by bringing up that the door was unlocked any time they could.

It should be pointed out that the question cites a case which is not an example of "Stand your ground law" but rather "Castle Doctrine" which holds that a person who has a legal right to be on private property has a right to defend themselves with appropriate force, up to and including deadly force. The primary difference between "Castle Doctrine" and "Stand Your Ground" is that "Castle Doctrine" pertains to private property you own or otherwise have a right to be on while the intruder does not. Stand Your Ground is allowing you to use force for self-defense in a public setting if you or another would be a victim of a crime.

Stand your ground law is the overwhelming majority of the Law in the U.S. with it being law in 39 states in the U.S (As well as 2 of the 5 territories). Of the remaining 11 (And D.C. and one Territory), 10 are Duty to Flee but give an exception to this Duty to Flee if one is one's home (and occasionally place of employment or even vehicle). Further, in Wisconsin and D.C., while there is no Duty to Flee, a jury may use the ability of the defendant to flee at the time of incident when considering whether they are using a valid claim of self-defense.

In all States, Castle Doctrine permits self-defense without the duty to retreate.

With that in mind, in the scenario provided, there is a valid claim of self-defense as the homeowner did not invite the maid into his house despite her mistaking address. In fact, there are cases such as this one where two Maryland Police officers were shot by the homeowner while serving a warrant to the wrong address. The Homeowner did surrender after learning it was the cops and because they were not legally allowed to enter his resident, he was not prosecuted for his actions. Both officers did survive the incident. Maryland is one of the 10 "Duty to Flee" states.