Breeding aside, I'm quite concerned with how much you're paying. We used to 'stud' our Cocker out to a breeder so have plenty of experience with different breeders and the most I've ever seen paid for one is £650. However, this litter's dad was a 3x Crufts champion and their mum had won several major competitions too. These pups were bred purely for showing so were obviously worth a bit more.
Bred dogs are often fairly inbred, but just to point out if they share a grandad they're first cousins, not 2nd. Which when a breeder can't work that one out is fairly worrying.
Do you know anyone who has bought a pup off her?
Did you spend any time with the parents of the dog?
Did you check about any health problems that may be in the family? Eye problems particularly, but also skin problems. Also, ask about the mother's bladder. Cockers can forget to hold it in when they get excited and it's often hereditary.
Did you spend any time with the puppy to get a grasp on it's personality? With a dog you want to go straight through the middle. You don't want the most out going in the litter, mischief is cute in a puppy but it can often turn into much more as an adult. Same with the shyest in a litter, it starts off cute but can create oroblems as an adult.
Have you seen the papers for the health check?
Have you checked they're definitely KC registered?
Have you checked their inoculation records?
Have you checked their tails? Are they docked or not? It's completely illegal in Scotland with a few exceptions, however in England working dogs and medical conditions are exceptions. So make sure you ask any questions if it is.
Sorry, I know you've probably checked every single one of those, particularly when you're spending so much on it. But I've seen far too many people get screwed over by dodgy breeders.