She wanted to hang out but then was "too tired"

I've been talking to this girl for a while and we've gone to lunch together a few times. We've been texting and I asked her on a date last weekend but she was busy. Last night we were texting and whatnot, then she said I should pick her up and we could go get something to eat. I was busy at the time but I said that I could in about an hour and a half. So then I text her about 1.5 hrs later and she says she still wants to go but she's too tired.

I was kind of piseed because I had other people trying to make plans with me and I told them I had something else to do. Could she really have just been tired just 1.5 hours later? I don't really understand.
She wanted to hang out but then was "too tired"
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