In the email from the breeder: Bunty is still registered under her name. The kittens are not registered under her name at all.
There are several steps you can take
(1) send the breeder a bill for all material expenses (food, damaged carpets, ect), your sleepless nights and time to take care of the mother and the baby cats, your loss of the lovely kittens that you have already bonded and attached closely ( in the case that you have to return some kittens to the breeder). This can easily exceed thousands of dollors.
(2) contact the organization that is in charge of feline registration in your area. Present your case and ask for their advices.
(3) different countries will have very different law
(4) read all paperwork you have signed-- is there any written documents where it mentioned that the purchase price is for A BARREN female ONLY? Most likely, there is none. Otherwise, the breeder will bring it up in her email.
(5) post in Law Forum for consultant
You don't have to be in a hurry to make the decision.