Girl's Behavior

What does it mean when a girl starts a text with ummm?

We were texting, I complimented her about something and she enjoyed it. I mentioned i was glad she enjoyed the compliment and then asked what she was doing that weekend. She responded with a couple blushing emoticons (I'm assuming from my earlier text) and then an "ummm" followed by what she was doing that weekend, leaving an opening possibly. I told her to let me know if that opening happened and I guess it never did.

The texting was going great up until that point. What does that umm mean?
What does it mean when a girl starts a text with ummm?
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