What would you do? Please read

I won't go into it all but for a little bit of background I will give some recent history. I ran her business for a year and a half while she lived 4 hours away with her then boyfriend, now husband, with the belief that I would take over the business. Last summer she discussed moving the business to her husbands town for several reasons but we had not made a final decision. She announced on FB that it would be moving and sent me a screenshot afterward and that's how I found out I was losing my job.. In the post she said it was so I could finish college, which I do online and would be doing either way. My boyfriend stood up for me and she called him and his family trash so needless to say they have not been around each other. 2 weeks after that announcement I found out I was pregnant but didn't look for a job because my boyfriend said I could just focus on school. I have lived with my boyfriend for almost 2 years and supported ourselves financially. In January I made sure she was not going to claim me on her taxes and said that my boyfriend would so we could get more from his tax refund before the baby comes. She told me I was trying to fuck her over in taxes etc. Again I have not lived with her or been supported by her. Her husband is loaded, she works for him and has her own business as well..

My boyfriend tried to reconcile and send her a message and she never wrote back to either of us. After that I ignored her for the first time in my life so maybe she would see how much she has hurt me. Because I want to have a somewhat normal relationship among all of us though I planned on talking to her again about putting the past behind us for the sake of our baby but that I would also not tolerate her talking down on my boyfriend. 

Before I could do that though, I got a letter in the mail that I had college loan debt from 2012 when I was a freshman. (I should be graduating this May but from changing majors/transferring I will be graduating next May) I have a twin sister and my parents are divorced so the agreement when we started college was that my dad would pay for my living expenses and my mom would pay for my sister's, because our tuition was covered by scholarship and grant money. (This didn't end up happening for all of our schooling though due to getting jobs etc) My sister did have a loan taken out that my mom said she would pay, although the loan wasn't really needed, but my dad and I agreed not to take a loan out for me because he was able to pay without a loan. So I was very confused when I got a letter 2 weeks ago saying I had $5,500 in school loan debt. I had the loan company send me paperwork to fill out since I had no idea about the loan for 4 years now. I ended up asking my mom about it and well.. She took it out, in my name. She went from saying that it wasn't intentional to saying that it was used for our car insurance and miscellaneous things to saying I got a lump sum check at one point which I did not and made me feel bad for being upset with her, throwing things up in my face from the past that were completely irrelevant. Again she won't own up to what she has done. She said that will pay it. Will that happen though? I'm not sure. I'm worried though because she has only paid $150 on my sister's $12,000 school loans that she said she would pay, even after her divorce from my ex stepdad where she got like $250,000 but bought a house.. She has also told my sister well I have my own school loans still. I am afraid that she will wait and say it's not her responsibility and dump it on us. And I especially am not in the position to pay. I have no job, not graduated, and I'm 31 weeks with plans of being a stay at home mom for at least a year while I finish school. My boyfriend is currently laid off at the moment too so money is extremely tight and all of our money is mainly going toward bills and groceries. 

In the paperwork I got from the loan company it says I have to provide a court verdict saying that it was identity theft, naming the guilty party. I feel stuck. I can't pay that loan, it's not my responsibility because I had no idea about it. But I'm just so tired of fighting with my mom. I want things to be smoothed out before the baby comes so he can have a relationship with his grandma and I don't have to stress over all of this bullshit. I love her, don't get me wrong she was always a good mother. I feel so guilty for having bad feelings toward her and worry all the time about if something were to happen to either of us that our relationship was never fixed. She is just selfish. I feel forced now to create more drama when I so desperately want to move on and everything be normal. But I feel like it's not really an option. What would you do in my situation? What would you do about the loan? Would you threaten her into paying it? Would you take her to court? I feel betrayed, frustrated, and just heartbroken. I'm sorry this was so long. I just feel like I need to hear unbiased opinions from outside sources. I would really appreciate any feedback, thank you in advance.