How interested do you think this girl really is? Need opinions?

[paul d]

My friend tried to set me up with this girl we sorta work with. He told her I was interested in taking her out, he says she smiled and gave him her number for me to call or text sometime. I've stopped over to visit her a few times, and shes not normally shy, but around me she's quiet, looks down a lot, very little eye contact, conversation is alright sometimes awkward others. I had to get her number again, when I asked for it, I noticed she had a big smile for a second or two. Yesterday we talked briefly and she mentioned she wasn't doing anything for the 4th when i asked, not sure if it was a hint or not, so I called her up an hour later or so and ask if she wanted to see fireworks but she says she just made plans. Normally I can read girls quite well, but this is a mixed bag for me. She gave me her number, shes nice when we talk, but despite all that I sorta get the vibe she isn't too into me, unless she is just nervous? So, do I ask her out again, or whats the best way to proceed?