I know it is okay. Many of us miss your point.
Oh well.....I don't get the people who prefer to shoot off one liners instead of giving well thought out explanations for their point of view. I realize that sarcasm and snarkiness is easier, but if you have become so cynical that you are unable to read what someone said, think about it, and then give a well thought out response, then what it the point of even being here?
I made a valid point. If there is no lease, and no compensation, at what point after someone voluntarily leaves (whether they take all their stuff or not, whether they gave back their key or not) are they no longer a resident subject to landlord/tenant laws? There are literally no laws that govern this. If one wants to insist that its based on keys and stuff, then someone could literally remain a resident for years. There are also no laws that state that this kind of resident is entitled to a key to the home. Even in situations where there is a lease and compensation there is nothing stopping a landlord from changing the locks. The landlord's responsibility is to provide a new key to the tenant.
Therefore, there is no reason why this OP's mother cannot change the locks in order to have some measure of control over the situation. The OP's mother certainly cannot sell or dispose of the belongings of the person in question in this short amount of time, because it clearly does not yet constitute abandonment, but there is NO reason at all why the locks cannot be changed.
Even without a lease when compensation is involved its much easier...because there is a measurable time frame, month to month, week to week, day to day. We are not talking about kicking out someone who is there...we are talking about not letting someone back in who voluntarily left and who has not paid compensation for a measurable amount of time.
Can someone who rented an apartment in an apartment complex leave at the end of a notice period without returning the key and leaving some of their stuff there come back three weeks later and demand entrance and residency? Of course they cannot. They can if the notice period hasn't ended, but they cannot if it has. Why in the world do you think that someone with no lease and no compensation must allow someone to re-enter at will and claim residency after they voluntarily left? What gives them a greater claim than someone who actually pays compensation on a week to week basis, for example?
In any case...the OP's mom has every right to change the locks. Any landlord has the right to change the locks. The question is whether or not they have to provide a key to the former tenant. I sincerely doubt that a homeowner has to provide a key to someone who voluntarily left 3 weeks ago, who had no lease and paid no compensation...and who wasn't married to the homeowner.
If you disagree...then feel free to explain why you disagree.