Typical HB annoying pattern

Happened to me couple times, they always change their mind if you give them time to think about it. There could be million reasons for it to happen: she meets someone else, she's insecure , etc...
I came to adopt a policy that if she said she wants to take it slow, never compromise with it. You want to stay in control, if you agree with her, you're giving her the power to take the lead and control the pace. I usually just ignore it and tell her "Look, we're adults, we will do whatever we are comfortable with" or I just tell her I will move on and if by any chance we run into each other down the road, then we will see.
I don't think you're moving fast at all, you've been seeing her for couple weeks, it's not like just for couple dates. The problem lies with her, and if she can't make up her damn mind, I wouldn't waste my time on her.
You need to stop acting needy, and freeze her out. If she does like you, she will be crawling back to you once she realizes you won't tolerate her BS and WILL walk away if she doesn't learn how to behave.