Some rabbits much prefer to be alone than to be with other rabbits. Since Willow is attacking any bun she comes into contact with, I would assume she should be a single bun Spoiler her with love and attention often, and she should be more than content.

I agree with Mikey – some just will not bond. Given the amount of bunnies you have introduced and the fighting that always occurs I think bringing another home could cause her more stress than good.
From my experience ( with dominant males lately ) the stress can bring its own issues ( territorial behaviours and illness )

I have a Lone Ranger – and he is much happier that way

It can be a long process but most buns want company of another bun. It’s very rare to want to be solo. Although speed dating can work, it’s not always the best option because for some couples it takes a lot of pre bonding which obviously you can’t do when speed dating. Pre bonding helps each bun become accustomed to the other’s scent and presence without feeling threatened. I wouldn’t give up if I were you tbh, I’d wait another month or so and see if your girl calms down a bit (it can take up to 6 months for hormones to disipate) then bring a bun home and let him/her settle in. Then do A LOT of pre bonding.

If you’re keen to have a pair, then Id revisit this again in a few months time. She may just need more time post spay. At the shelters, do they introduce the bunnies out in an open area where the other rabbits enclosures are? Or away in a small room? Perhaps them meeting in a quiet office or even in a car would give a better idea. The sights, smells and sounds may be affecting her somewhat.

If bonding is not going to work out for her, don’t feel too badly. Do you work daytime hours? In my experience, rabbits spent a good portion of the day sleeping.