I think you already gave yourself the answer in your own case:
Because I give zero crap about what other people think of me.
This applies to people that aren’t in your inner circle. You want HER to be in that circle and suddenly it actually does matter what SHE thinks of you. You have little to lose with people you don’t really care about, but everything to lose with people you do care about. It’s an evil social twist that makes everything so complicated. High self-esteem is just the ability to quickly pull yourself up when you fall and the knowledge that you actually CAN do so. It mitigates the risks of “putting yourself out there”.