Assuming/taking over a mortgage

[Connor Williams]

My wife and I want to purchase her moms house and let her live there rent free. We would be purchasing it for her mortgage amount. We can’t assume the loan. 

What can we do to avoid the 8+ percent interest rates? 

Add ourselves to title and let her keep paying the mortgage and reimburse her? My worry with that is she buys something, doesn’t pay for it and becomes a lien. Or would we have to sign off everything since we are now on title?