First rule of preforeclosure investing is to never let the seller stay in the property. Violate this rule and you will most likely get burned.
You need to evaluate it as a regular deal, is there enough equity in it to resell the property? Can you wholesale it? You could probably get an option on the house and then try to find a buyer and collect a fee that way, assuming the numbers work of course.
What happens if she could not pay you in couple of months? are you going to evict her? she could not make the payments on her current mortgage, what assurances do you have that she will be consistently pay you.
I know you want to help, but you also have to look at it from your own selfish standpoint.
If she is having trouble paying the bank now, what makes you think she will be able to pay you? If you are taking out equity, how will your payments be lower than what she currently owes? And how could you make the property cash flow without the payments being higher?
And what will stop her from taking advantage of your friendship to be late with payments, or coming to you with never ending stories of how she will ’ have the payment soon, next month will be better’… blah blah.
If she can’t keep up with payments, are you willing to evict? It’s usually best to not do business with friends.