I'm not sure where the opportunity is in this scenario. I get the sense you decide you wanted to get into investing, looked around and saw your mom's townhouse and are now trying to make a square peg fit into a round hole. It also sounds like she has no interest in having a rental and she's being convinced to be your guinea pig.
From my reading of your question, I think your mom is a traditional home buyer (sell her current place and buy a new one). I think she needs to find a new place that fits her needs and get the best financing she can. Then, if she has money left over and she wants to act as a private lender, she can invest in an opportunity you find.
I think if you try to do all sorts of financing gymnastics to try and make something work, it can turn ugly. And if your mom isn't totally on board (i.e. she doesn't want a rental property), it's going to cause more issues than just possibly losing some money.
I think borrowing money from older people is riskier than borrowing from younger people. If a 30 year old loses 60k, they've got lots of time to make it up. If a 65year told loses 60k, they may not have a place to live much longer.
Good luck.