First off, do not bring another rabbit into the picture until you and Bea overcome this issue. Another rabbit isnt just going to sit there and take it when she lunges and digs her nails into them, theyll fight back which can lead to severe wounds or even death. For everyone involved, its better if you dont speed date her until this is fixed either, since you cant bring the bunny home that she picks out, anyway

I would first go to the vet and see if there is something going on. Some rabbits get random surges of hormones, even after being fixed. They usually go away after a few days. Another reason to see the vet is to make sure shes not acting out due to pain or discomfort. After the vet gives her the clear, you should start with clicker training. When she starts to chin mark, use the clicker to call her over then give her a toy that is hers and only hers. You can try treats, but this may cause her to think chin marking is a good thing, and make the problem worse. This will take a lot of practice and patience. I would say if it doesnt improve after a months span, try another form of redirection training. If that doesnt work after another months span, assume being territorial is part of her nature and she may not grow out of it

6 weeks can be too short time for a spay to take full effect in a girl rabbit. They tend to need more time than the boys. Territoriality is classic hormonal behavior, and as Mikey says, it’s not uncommon for buns to experience random hormonal surges after being desexed. In rare cases girls can need up to 6 months.