Guest, I assume you are in the UK since you refer to the GCCF.

This is a lovely offer and acceptance/consideration question. These are technical issues of English contract law. It all depends on the order in which things happened. If I get the order right (it all depends on that) I think it works out like this:

You went to see the kitten. No contract so far.

You discussed the kitten, the price and the pedigree papers. No contract so far.

At some point the seller asked you if you were going to breed the cat.

That must have been in the context of the pedigree papers because the main reason for having pedigree papers is to be able to register the progeny.

Whatever was said in those discussions COULD have amounted to representations, but I don't plan to go there as in context I think the relevant things will have become part of a contract, see below.

It can (surely) only have been after that that one of you said "£300?" and the other said "OK".

At that point a contract came into being. Nothing said after that can be part of that contract - and it can only be part of a later additional contract.

The express terms were cat, £300, no breeding, no papers.

What about implied terms? The seller it seems is in trade breeding cats. I think a cat must be "goods" for the purposes of the Sale of Goods Act. So by S. 14 (2) there is an implied term that the cat must be fit for "all the purposes for which goods of the kind in question are commonly supplied". It is settled law that "goods" include instructions and that would I suggest apply in the case of a pedigree animal to its pedigree. But see S 14(3) - the implied term does not apply to matter "which is specifically drawn to the buyer's attention before the contract is made". So that doesn't help you get the papers.

Did you make a collateral contract as you were leaving - to the effect that she would send on the papers? No. The reason is this. You already had a contract (see above). To make a new contract there would need to be "fresh consideration" - in this case something in it for the seller as well as something in it for you. There are new-ish cases about "practical benefit" but I don't think they affect it.

Upshot - there is no contract for her to send you the papers. There is a contract for you not to breed the cat, but it's oral and proving it might be difficult.

This is not solicitor-client legal advice and no duty of care is accepted.