if you dont have her number then you would have to create a chance bump-over meet with her. After which you can play by the rules of the game.
If you have her number then, try with some statement that does not display neediness, rather shows you have a fun life.
something like..
Just went thru my phone book and could not tell if [her name] is a guy or a girl. Can you please double check and let me know. I plan to delete your number if you are a guy lol

P.S. - yo watup [her name], i did not know you knew my fren Kelly...!!
this works better if she has the most obvious girl name like katie, or julie etc.
now you dont actually have to know kelly... it is just a bait of curiousity, for her to pick on. It creates mystery and keeps the frame control to you.
Remember = Dont disclose immediately in the next text that you dont actually know kelly, like some AFC chump. Keep the thread on until you set up a meeting and then playfully use it to your advantage showing that you are witty and fun to hang around.
If she does not respond then, try something like --
Hey [XX],
me and my frens ~ going [YY] tonight ~ super fun ~ you can tag along if you want.
This is the best i can surmise and advise from here, reading all you have described in your post lol.
some details might prove helpful though.
anyway, lets see how things go after.
_________________
-- Jack
Patience and Calibration are the keys for the perfect seduction
[++ reputation if this seems the right thing to do

]