ask her for a coffee.
it puts less pressure on her, and on you- it will be for about an hour. if you go for a meal, it will last longer, and maybe have the need to dress up more- its more formally a date, too. and in the evening, there is omre of the 'do we kiss afterwards??' issue, which doesnt come up so much on say saturday afternoon...
if you do it during the week you could do it at lunch time, so you would know you definatly have to end at a certain time (so you can escape if its getting a bit stressy), or do it on weekend if you think you'd like to perhaps go on somwhere afterwards.
dont worry too much- if you know somewhere realy nice you could suggest that, but you can also ask her if there is anywhere she'd like to go.
good luck! you DEFINATLY can be sure she likes oyu if she gave you her number- it must have taken some confidence for her to do that. cool chick.