Hey, Luna is a lovely girl.
From your description of her, Luna does sound like a girl.
Adding another bird will change the dynamic.
The most important thing would be to quarantine your new bird and work on a bond independently during this time, and then keep establishing the bond once they are together.
It's really important to consider the full implications before making a decision. If she's happy and you're happy, then adding a new bird might be avoided at this time.
If her bond with you changed and it would upset you that much, it might not be worth the risk. There's also the slight chance that the friend you got for her wouldn't be a good fit and you'd have to house them on their own.
Two girls could get on fine, it's all about personality. The same is true of a male and female.
As for introducing them, after quarantine, it's best to take it nice and slowly and make sure they meet in a neutral location (out of the cage).
best of luck.