
I should say first that I'm no Cocker expert - I'm a big dog kinda person ;)
Having said that, the best advice I could give is to _take her time_ - cockers are unfortunately one of those "victims of their own success" type dogs - they are such good pets that they have been overbred, often by really bad characters with little thought for their health.
Things to check for: make sure both parent dogs have had their eyes tested and certified healthy by a professional; check the pedigree of pups as well, you want as many dogs in it tested for this as possible. Cockers have a few bad eye problems, most noteably Progressive Retinal Atrophy - basically cateracts, meaning the dog goes blind. It can happen young a well. Eye deformities and absence are not that uncommon either - I am a dog groomer, and I have one blind cocker bitch (cateracts) and one blind cocker dog (cataract + one missing eye - he never had it, was born blind).
Also you want to be sure of temperament. Cockers are known, though thankfully not too commonly, for suffering a thing called "rage syndrome" - this is bouts of random, unprovoked severe aggression, also with no warning signs before an attack whatsoever. It can be dangerous and devastating, especially if there are kids involved - even if they don't get hurt, the only course of action is euthanasia, whcih is of course very upsetting. The best way to avoid this trap is to only buy from a really good breeder - go the www.the-kennel-club.org.uk, and email them, they can send your friend a list of all the good breeders in the country. Rage Syndrome suffering cockers are typically from bad breeders - one case involved almost every pup in a litter suffering it; the litter was bred by a commercial breeder (aka. puppy farm). A groomer I know also suggested that red cockers tend to have more temperament issues than other colours - but I have no idea if this is true, and honestly I wouldn't worry too much. She said some odd things :)
Otherwise, check for good health - find out if the parents have had many ear problems (another thing they are prone to, because of the hanging ears and long hair); I don't know if it's genetic or not, but it pays to be safe.
Can't think of much else... hopefully if there is anything someone else will post it for you. Good luck to yoru friend - and tell her to be patient! Cockers are popular, it could be that the good breeders have a bit of a waiting list. Shouldn't be too long a wait hopefully - lots of breeders around. When she does get one, she should be sure to get it to a groomer as soon as possible, to get it used to being clipped (if she wants it clipped) and handled - I can tell you, a fidgety little dog is a right pain!