[Can someone tell me I'm being irrational so I can just appreciate this high without guilt? Lolol.
What you're describing is "manic behavior", which is a trait associated to bipolar. My daughter has a dual diagnosis of BPD/bi-polar and I think her mom (my ex wife) would have the same diagnosis.
When someone is manic, everything is wonderful and they're impulsive, flirtatious, carefree, etc. Every day is the best day ever! And if this is what's happening, then you absolutely can just enjoy it...with a few warnings. Make sure she's not putting herself in harm's way in terms of spending, driving, making new friends, etc. She's not thinking clearly and it can be dangerous.
The opposite of manic is depression...which you said she was stuck in for a few months. Part of that is chemicals produced in the brain, so this is a real thing. Just know that even though she's way way "up" right now, what goes up must come down. So be prepared for the coin to flip rather suddenly.