I think the previous answer is mostly correct. To explain about the girl's use of から a bit more, with her use of から saying "will you meet me tomorrow? .... (Because) I will say it tomorrow" - so から indicates that "I will say it tomorrow" is the reason why she is asking to meet up. So in English a less awkward way to say this might be:
"Will you meet with me tomorrow? Cuz I'll tell you then"
"I'll tell you tomorrow, so will you meet with me then?"
から can also be used to "soften" the end of a sentence. It makes it more approachable or amiable in a way, in some contexts. Sort of like how some people add "lol" at the end of every sentence when they text, not because they think something's funny but to convey that they are not using a cold, bored, or upset tone.
Another way to think about her response is to think of English/your native language. This doesn't always work, but for this situation I think it might help. In this case, if she was speaking casually in English she may say something like:
"I'll say it tomorrow so..."
While not grammatically a full sentence in English, native speakers often talk this way. It would not be unnatural for someone feeling shy and awkward to trail off at the end of this sentence.