There is no specific requirement for her to have a job in Poland in order to visit the US. The most relevant information can be found on the Nonimmigrant Visas page of the US Diplomatic Mission to Poland.
The most important thing is probably that she will need to demonstrate that she intends to return to Poland at the completion of her visit. This might be harder to show without a job, but it should still be possible.
A visitor to the US may be required to show proof of sufficient funds to cover their stay in the country. I don't know what this amount might be, or whether it will be required for somebody from Poland staying for a couple of weeks. The best approach for her would be to start the online application process and see what questions it asks.
If the application asks what the purpose of the visit is, I would suggest keeping the answer simple, such as "Visiting a friend" rather than "I met the love of my life and I'm going to the US to live with him for several weeks".