I was an international student and graduated 3 years ago. Now I want to continue my research career instead of working in the industry. I worked for free for a professor for one month last year. It was a good experience and we had a good impression to each other. I approach her again and asked to get back to her lab, she said that she could consider to work together on a project for 1 year, but she has no money. On one side, I was always excited about to be back to a lab to do more researches, and expecting to extend it to a phd study; on the other side, I couldn't be glad and work well without enough money. I am going to meet this professor soon, I was wondering:
Why did she asked me to work for free?
How to negotiate or should I just give it up?