Have you banged her? Dated her? Gotten her number? Called her?
Not trying to belittle you, but it seems like she's just some chick who you like, but has contributed nothing to your life. So, I guess i'm just trying to say...who cares?
And I'm not saying that in a mean way. I'm just saying, okay cool...she flirted with you. Is that it? Is that what's causing your mind to swirl with all these questions about her? Girls flirt with me all the time. Sometimes that's just how they are. It's not always a guaranteed bang.
And christ, she's a trainer. She's trying to sell herself. In every gym I've been to, I've seen the girl trainers float some flirty vibes at guys. And I've seen guy trainers do the same to girls. You sound like those guys who are blown away when a waitress flirts with them, but doesn't go on a date. Yeah, when you're in a position of selling yourself to the public, you better be super friendly.
...and even if I'm wrong about it, and you think she's only flirting with you...still...who cares. You've lost nothing because she never gave you anything in the first place. Why has she gone cold? Who knows. Either you did something, or she's a typical crazy female...or maybe she's just an as*hole. Either way....the fact that you care so much about this worthless, useless woman tells me that you're not talking to enough girls in your life.