You're 15 and this is irrelevant to your future.
If you act really pip and cheery the next time you see her, there will be an instinctual, primordial gut-wrench that makes her feel like she made a mistake (because you seem unphased), and she'll lust after your alpha male gonads like a hungry spider.
This actually.
When me and my ex broke up (we dated for like 16 months) and I was completely unphased by it (or at least to the naked eye, I was a little dead on the inside :3), she saw it and was begging for me back basically (she broke up with me).