Is there a reliable way to dramatically increase hair growth?

I am posting this for my (still) unwired girlfriend (this is how things are when you live in Poland...)
She recently cut her hair from around mid back to 3cm below her ears. This radical change did not bring the much wanted outcome. In fact, she wants to grow her hair back as fast as possible. I guess it is imaginable to think of the former length in a matter of weeks or months, but are there any reliable lotions, pills or other staff that can significantly increase growth?
My girlfriend's hair is thick, straight and dark brown, rather silky albeit too short. You can answer here or to my e-mail.

Thanks,
Amir