When a family member uses your credit card without premission it's fraud. I understand, it's a hard choice to make. But, look at it this way. If she did this to you once, there is a good chance she will try and attempt it again.
Even if it doesn't happen again, your credit right now is fucked. Takeing out a loan, to pay off the $700 isn't the answer. Your just opening another line of credit, not paying off any debt.
First, you must talk to her. If she isn't going to pay this back, or can't pay this back you must take action. Now, this could be fileing with the credit company, and possible legal action. This could be you asking another faimly member to help pay these bills, this could be you working a extra job for the next 4 months.
Bottem line is, don't let this debit add up and DO NOT open another line of credit to pay off this line of credit.
Jay