Booster.... you need experience to answer her without giving yourself a complete guilt trip, I can tell from the way you ask the question.
Want to know a great way to learn some phrases against her?
Go and ask out 20 girls... if you really want to be just her friend, and don't want to hurt her feelings, play female games... They are far more adept than most guys at rejecting men.
If you want, you can try and make a new kind of opener with it. Some what of a Jealousy Opener, somebody else did a "I want to get rejected" opener that works like a charm every time I use it.
Talk to the girl, and don't screw anything up, just respond respond and talk, no escalation, and keep it calm and mysterious... just be you, whatever kind of person you are right now...
BUT you going to have a purpose, and you will remain congruent the entire time!
What is your purpose? TO choose THE worst moment to ask her out.
When is the worst moment? In the middle of fluff talk, right after you give her a compliment, and right after she laughs at one of your jokes.
Don't foget the field report so we can judge how well you can follow orders.
Cheers!