You can sue her if she does not pay you back. However, you have to prove the terms of the loan and that it was not a gift, which is likely going to her defense. It would be better if you had something in writing.
Do you need a lawyer? No, but you don't NEED a doctor either. This is going to be complicated. For example, do you file a limited civil case or an unlimited case? Do you serve discovery? How much discovery can you serve? Are you required to attend a CMC? Look, if it were easy, we wouldn't have lawyers. But, its not. So we have lawyers who are professionals who do this all the time.
If you don't want to hire an attorney, most of whom who do this on a contingency basis, then plan on spending a lot of hours at the law library learning what we learned in school.