New bunny terrorizing old one.

Hello all. So here's my concern. I have a 4yo Mini Rex neutered. Been wanting to get him a buddy for a bit. Friend says his GF is getting rid of their bunny because kids aren't giving it attention.

She is unspayed 6mo old flop. I set up a meeting. She's calm. They get along. Occasional licking, sniffing etc but mostly mutual ignoring. I decide to take her. The next day they drop her off. First half of day, same thing. She gets steadily braver and more sure as she explores. Now the new little hellion is terrorizing my rex. If they're both out she insists on chasing him and trying to mount. I mean she GOES after him. Like picture pepe le le pu but with the road runner's speed. Right now she's pawing at his cage to get to him, pooping on the carpet ( I know marking will stop after she's fixed.) Is this normal? I can't have them both out. I'm moving soon and don't think I could fit two cages where Im going. My vet offers bonding services, but it'll be before I can get her fixed. The vet says it shouldn't matter the order I do this in. He seemed to like her until she went crazy, so I'm still thinking they can bond successfully.

On an ironic note, they got rid of her because she wasn't active and the attention she received suffered for it. It's pretty clear they didn't give her space to run, cause this girl loves to run around and explore when she's not freaking out my rex.

If your vet meant to say that it doesn't matter whether they try to bond her before or after fixing, then he is dead wrong. A rabbit needs to be spayed before attempting to bond -- especially if she is behaving as you describe. Any fights they have now will greatly diminish their chances of bonding in the future.

The two need to be completely separated for now. Try to find a place to put her that is somewhere you will not be having both of them later on. Females can be terribly territorial so you don't want her claiming an area that you eventually want them both to share.

Once she's spayed and healed, then you can begin some pre-bonding. Moving will actually be to your advantage. If they are pre-bonded, then the new place will be completely neutral so they can bond together there.

So until she's spayed and healed, they should have no contact whatsoever. Hopefully they will forget that they tussled. This waiting period would be a good time to read up on bonding procedures (honestly, I would not trust that vet to do the bonding based on what was said). The following website gives some fantastic, thorough advice on bonding:
https://www.cottontails-rescue.org.uk/information/bonding-bunnies/

There are even videos there showing various bonds in progress.

Thanks for the info. Unfortunately even if I have her spayed tomorrow, I'll be out of here by this weekend. Best I can do to is keep them locked up in their cages while the other is out, see how quick the vet can fit her in for spaying.
Should I spay her asap even if recovers here for a day or two and I move ( thus having to move her while in pain?) Or should I bring her in and time it so I bring her home after I move?

That's a tough call. If you bring her home right away, she'll be in familiar surroundings but will stress with the move. If you bring her directly to the new place, it will still be stressful. Perhaps bringing her directly to the new place would be the better option.