The mortgage was in her name (long story).

She just wants to stay in her apartment until the lease is up because it's going to inconvenience her because she has to buy things for the home.

. - A bank won't give me a loan because the house is in disrepair/needs 50-100k in rehab.Possible solutions that may come with their own set of problems:- My fiance buys the new primary in her name.

What obstacles could I face in this process? 

There each investor should be thinking on what the amount of earnings from the transaction would make it worth or not to be invested in. Here

(which is better for her because the property stays in her name till I pay it off.)

I assume since you're in here, you work with investors?

The old rule used to be that all 4 units rents had to meet or exceed the monthly obligation but recently within the last year or so they started discounting this monthly income and still required borrowers to meet or exceed the monthly obligation which inherently makes it harder for higher priced markets to obtain FHA loans on 3-4 unit properties.

I'm sure a someone from Dallas will drop in here soon.

I have found a vast majority of people in here are in this part time and looking to get into it as a full time venture.