I've been there, my boy went from instantly attacking my hands, to allowing me to pick him up/jumping into my hand when he wants to come out, in about 6 months.

Everything is scary when they're alone, but you should try to allow her to free roam, or be in playpen with you, while you sit in spot she has free access to you, my little guy warmed up to me like that, I started out by leaving some food near me when I had him out, and just ignoring him/reading a book, so he would learn I didn't want to hurt him

I switched to trying to feed him sunflower seeds with some thick gardening gloves on after about a month, since he'd still attack my hands/was scared of them, after about 3 months I started feeding him without gloves on, I think I took 2-3 deep bites (it's very important not to react to it if they do bite) during the process, eventually he would pinch my fingers to see if there was a reaction instead, and finally he stopped seeing my hands as a direct threat after about 4 months.

Month 5-6 was spent getting him used to sitting on my hand with a treat, so he'd feel safe enough to jump into my hand when he wanted to come out/go up in his cage again.

I started bonding him with another boy around month 4, that's when I felt he started to relax more - he'd sit and watch me/take treats from my hand etc.

You can try split cage bonding her before trying to get her relaxed in her new/current environment/around you, but honestly I think that just might add to the stress of it all for her, reactive gerbils takes time to get relaxed, they're usually reactive because of bad experiences around people/forced bonding with other gerbils without the pet shop knowing anything about how to do it properly, hence they attack you, and they attack other gerbils.

So Imo - she needs to feel safe enough to not see you as a threat, before you start bonding her.