To be sure I understand,
You are absorbing $18k worth of debt, plus $1100/yr in taxes and I'm guessing $1100/yr in insurance and in return, you own a house. But your mom keeps 100% of the rent. The house has no mortgage or liens on it. Did I get that right?
Who pays for the repairs? Not just the little things that chip away at you $100 to $200 at a time, but the big things like the roof, the HVAC, carpet, painting, a trashed place from a bad tenant? Property management fees? Umbrella insurance to protect your assets from a litigious tenant or tenant visitor? Eviction court costs? Return of the tenant's deposits and excess rent paid?
(Hint: if your mom needs this kind of help with her finances the answer is "you".)
It's great to help your mom, just make sure you know what you're signing up for. And recognize that if you don't have the right legal paperwork in place, a judge ruling on behalf of a tenant can take it out of your pocket as the property owner...
The other part I'm not sure I understand. This is a personal loan or a HELOC? One is secured by a property (presumably this one) and the other is not. Depending on how the line of credit is set up, she could take money out of it as fast as you put it in. So, when you say you're "taking it over", what do you actually mean?