@MochiBall has he spent much time at their house?
If not, you could be correct about the "abandonment" concerns. But if he's accustomed to her and the environment it shouldn't be a big issue
@MochiBall tell her it has to be a trial for a couple of days...
Or, perhaps take her to a shelter and let her pick out a puppy (or a young dog as training may be too much for her right now) that you can adopt for her?
@NapsAndSarcasm he’s been to their house quite a few times and they here of course so she’s no stranger. My poor mother in law isn’t doing well at all and I think this is the least I can do. But, this house thinks of our dogs like our actual family members so I get worrried but you’re right. It probably isn’t a problem….