If you ask a girl to go do something with you, like going to a sports game or bowling or whatever, and she says "I'll let you know" is she just letting you down gently? I told this girl to let me know in two days and she repeated "two days" but from her tone and body language, I'm not sure if she's seriously considering it.
Actually, guys, it turned out that she eventually said "yes" in two days. Maybe she was just old-fashioned and needed to check with her parents or something. Or maybe she really had to think about it.