When you get a number close and text a girl to meet up, it's pretty common knowledge that a girl being "busy" all the time or unavailable is a sign she isn't interested.

However, what can one do in a situation in which the flake is ambiguous.

I recently asked a girl on a second date after a fairly decent first date. I asked when she was free over the weekend, and she answered "I'm not sure yet".

Is this a flake, and I should delete and move on to the next one?

Is there anything I should respond with, or simply let it be?

EDIT: Additional info, not sure if relevant: English is not her first language.