Look at it this way. You have nothing to loose! She isnt yours now, if she says no then she wont be. If she says yes then it may develop into something. Just man up and ask her out! Isn't she worth it?
u just need to gather ur bravery and ask her out, i remember when i was always nervous ad shy around girls. but i eventually just went for and asked one out. now its easy as cake to ask girls out.