You jumped the gun. Didnt create any comfort even if she was attracted to you.
Next time what you want to do is shift the frame to you, if the girl says something that reminds you of an experience or related topic, use that as a dhv. Otherwise try to take something she said and use it to joke around. (example: "O you give presentations, you're not one of those stuffy office working types, cubical and all, are you?...I hope not im just the social type, i like to get out and meet new people, and working professionals always seem to be too into their work for anything else.)
When you start receiving definite signs that a girl is interested in you, then its fine to try and elevate things to another level (phone convo or meeting). Usually id recommend to take it a bit slower, try to get the number, then try to meet after youve talked a few times. You'll be surprised, but ive found that most girls will throw their number at you if you create attraction and comfort right online. The last 3-4 girls ive connected with online in a row, gave me their numbers without me asking.
My recommendation would be to ignore that she didnt give you the number and couldnt meet up...instead use this as an opportunity to create some comfort and dhv. Make your response light hearted, as you want to come across as unbothered by her response. Who knows, if you create enough comfort, maybe her travel plans will get "canceled".
You could probably even go with something along the lines of the example i gave you.