Change in behaviour, timid cats become a bully

[Justonedayatatime11]

When we first got Flick home 9 weeks ago, she was very timid and shy, scared witless of my other cats. However, she's now billed up quite a bit (possibly too much) and has become an absolute nightmare. She's really bullying my tiny little white cat, who never starts anything, is entirely incapable of standing up for herself and is terrified of Flick.
I can think of any drastic changes we've had to explain the sudden change in behaviour but I don't know what to do about it. Her breeder was adamant she was very shy, and normally got pushed about by other cats so I wasn't expecting this

She probably needs to be the only cat in a household and it might be kindest all round to re-home her. Something similar happened when my DSis took on a rescue cat as company for her other cat after his DBro disappeared. She had to get the RSPCA to take him back as he was terrorising her other cat. She got a cat behaviourist in before taking that course of action and the RSPCA were reluctant.

How did you do initial introductions? Two months in is still early days and sounds like they are sorting out hierarchies.

What form does the bullying take? Do you have enough resources (food/water bowls, litter boxes, cat trees, beds etc.) to have 1 per cat + 1 extra?