Asking out by email is a bad strategy. It displays lack of courage which is never an attractive trait. But worst of all is the hideous wait after you have sent the message, which gets worse and worse the longer the delay before (or if) you get a reply. Far, far, better to push forward nerves and all - afaint heart never won a fair lady etc.. - and ask her out face to face. You get immediate feedback. and ultimately what ever happens it feels better. Good luck.