You should definetly ask her out and remember you have to ask her out for a specific day, place, and time. It sounds like you are waiting for lauren to make the first move and some girls just won't do that. They want an assertive male that knows what he wants. You've got nothing to lose by asking her out on a date only two things to gain. One is you will know if she lieks you and you won't have to keep wondering about it, two is you'll have a date if she says yes.
And about her just laughing it off that you like her. Girls do that sometimes so as to not seem desperate and secretly think wow. Plus she doesn't know if you're friends are just messing around with her and what would you expect her to say in front of them anyway?
Ask her out!
One day the Moon said to me, "If he makes you cry, why dont you leave him?" I looked up at the Moon and said, "Moon would you ever leave your sky?"