If you know her, like you have somewhat connected and you feel the IOIs, I don't see the point of making a big deal out of it. Just ask her out.
You will notice this, that in most of my posts I recommend guys to stop complicating things.
Here is how I would do it, whats a good place where you would like to take her? like a cool bar, or a great vista point, a park, whatever you think she would respone best to.
Tell her about the place in one of your conversations.. Like " me and my friends usually hang out at this bar/restaurant and we always have a good time because...."
Ask her if she has been there, her reply dosen't matter unless she says her dad died there or something extreme
Tell her "we should go there together sometime" make sure that all your stories and lines sound convincing and appealing, practice in front of a mirror if you need to.
Now she will say yes, even if she isn't sure yet, she will say yes because you sound so convincing she cant say no.
And then you just say, "great whats your number?"
See, simple and straight forward!