What are some good foods/vitamins/hair products, etc to help my girlfriend's hair grow faster?

I've been with my gf for about 2.5 years almost. She knows of my fondness for longer hair on her and it's gone from touching her shoulders when I met her to just about at BSL now, so let's say it's 24" today. She has since started using higher quality shampoos, etc. and it's beautifully thick and resembles a gorgeous chocolate waterfall. Obviously I find her much more attractive due to this as a result, or I wouldn't be here, LOL. On this subject, she's said "I don't mind long hair, just as long as I can't sit on it" and "why would I cut it if you like it longer?" I also know this is the longest she's had it in her life so that's welcoming also. She even (finally) discovered recently when we were intimate, how arousing it is for me when her longer hair drapes across my chest... and she said "I'm gonna have to add that to my repertoire!" (long story short, she's a keeper!)

Anyway, all that said, I'm not expecting anywhere from knee to floor length but I'll take waist length on her, definitely... but it feels like it's barely grown AT ALL in the last year (it probably has, just too subtle for me to notice) I know this is somewhat selfish on my part too, but as long as she's committed, I'm more than happy to help anyway I can, ya know? Surely BSL is not terminal for her. Surely...

So... any tips how I can help her out? Or am I forced to just... wait?