I am also 51 years old, and a woman.
I have been a legal assisant (litigation) in the United States for over 20 years. DO NOT do anything to jeopardize her tidbit business. You do not want to cause any problems, any more than you have.
As a litigation legal assistant, I have over 20 years of experience in litigation. I know the law. I also have a paralegal degree and took business litigation as part of my paralegal degree.
Straight to the point. Sounds good that you can get an attorney in Germany. If she is in Germany and her business is in Germany, that helps. Maybe the attorney can persuade her to pay you. How much is it going to cost you financially to even attempt to collect any money? It will probably cost you more than what she owes you. Whatever - Buddy - from a legal standpoint -
She is in Germany. You are in the United States. She has no legal obligation to pay you one penny.
I suggest you get a legal consultation from an attorney where you live, one who specializes in business law, and get a consultation. It may cost you about $300.00 (he won't do it for free) - and get a real legal opinion.
Do not do any more work for this woman. If you have work she is waiting for from you, tell her you will not be providing anything until you get compensation for your work.