How to get someone to gain weight

Ok my gf is REALLY skinny, how do I make her gain weight fast? I mean, I don't want her to be FAT, but she is sickly thin.

Go to GNC and talk to the people about weight gaining formulas.  They may suggest protien shakes or some of that other shit.  Or you can go talk to a doctor, and try to find doctor things that can help her.

THEN you need to talk to your girlfriend.  Tell her that you're concerned for her health because her weight is so low.  And tell her that you love her and that you'll love her, no matter what size or something similar.