I am a hair stylist and I always suggest optimum for hair and nails at high health. I've always heard of the prenatal vitamin thing and I think in general if you take vitamins it's good for your hair. You might want to compare labels but personally I would take the stuff formulated for your hair. I definitely noticed a difference from taking them religiously after a few weeks. I'm pregnant and on prenatals now and haven't noticed my hair growing faster, I think it depends on the person.
Someone suggested gelatin, that's probably a good idea. Also any stimulation to the scalp, it gets the blood flowing and your hair growing, so scalp massages!
FYI, I'm pretty sure Locks for Love requires 12 inches, and when you cut it off it's in a pony tail and you still need room for the haircut you want (unless you plan on buzzing it).
It's a very noble cause but make sure it’s what you really want to do. I would call Locks for Love and get more specific details, the owner of my shop is under the impression that they get so many donations they're not really in need (I'm not sure if that's true or not), and I've heard of people selling their hair for like $3,000 (again I don't know for sure, but it’s something to think about). You might want to investigate your options, but by no means am I trying to talk you out of it, like I said it's a noble cause, more power to you if you can do it!
Good luck!