The chances of you ever seeing the full amount are very slim. You should never loan money to anyone without a formal agreement.
If you want to attempt to get a portion of the money back...
You could go to small claims court. However, that only means there will be a judgement placed against her, it doesn't necessarily mean you'll get your money.
You could write her a letter threatening to take legal action if she doesn't make arrangements for a payment plan. Make sure you send it certified mail. Just the threat may get you some money.
You could also contact an attorney. You could pay the attorney a small fee to write a threatening letter.