somewhat recently i got a vibrator for my girl, but she we kinda discussed it. we were gonna get our 1st movie together and i asked her if she wanted a toy and she said yeah (though still kinda shy about it). she got shy and stayed in the car and i went in and picked one out myself, she liked it. i went with a normal white vibrator 7.5'' that came with a cock shaped rubbed jelly sleeve over it.
if you're no completely sure how she'll take it, go for the
normal small mini-vibe type things. its not all out there, low key and not too threatening.
something like this
http://www.sextoys.co.uk/modules/images/alt-images/N4431-Remote_Control_Mini_Vibe-1.jpg
if you are thinking about getting her a toy, im sure you have a decent sex life, so as long as youre already fucking, do it. it could be the start of something great.
if you havent had sex yet, id wait til you did. you dont want to scare her.
just go for something very basic. stay away from the dongs and huge cock shaped shit. introduce it slow and if she likes it you can go from there.