I am afraid it is a case of 'caveat emptor' (let the buyer beware).
If you bought her from an advertisement, and it said KC registered, if you can get hold of a copy of the advertisement then you have a case to take to Trading Standards. If there was no mention of KC registration then you have no case.
There is no reason for the breeder not to give you the registration when you bought her, as the KC now process registrations within days, and if the breeder had registered the puppy, but put endorsements on the registration (no progeny to be registered, no export pedigree) you would have needed to sign a form/letter/contract or something to acknowledge that you accepted these conditions.
If the breeder is licensed by the local authority (which she should if she has more than four litters a year) they may be interested to know about this but in all honesty I think unless you have something in writing to say KC registered or KC Registration to follow, then you have not got a leg to stand on.
You could check with the KC to see if the litter has been registered (0870 6066750) give them the name of the mother and the name of the breeder.