Mmmm - one that you are perhaps not going to like the answer too - but if she is so small then she's perhaps not a good enough example of the breed to use for breeding, unless she is perfect in every other way and so imho I think you should probably put breeding from her right out of your mind.
Do you have a specific reason for wanting to breed and from this girl? There are a thousand questions you need to resolve for example, have you bred before? Have you done a good trawl of the breeding section to learn about the pitfalls of breeding? Do you have the support of an experienced Cocker breeder?
Is there a reason why she is small? Is she just very light or is she small in stature too? Does she have fine bones maybe?
Have you sourced a quality stud dog in preparation?
Sorry that's a lot of questions but all, plus many more, would need the right answers before you should go ahead.
To breed from a bitch needs to be strong and fit and a good example of the breed usually determined either by show results or by the bitches breeder or other reputable breeder advising if she could be used for breeding or not.
If you've set your heart on breeding then if you've done the groundwork you'll have the right answers to all these anyway - but if not then you'll see how much more work you have to do - let alone ensuring your girl is OK to breed from.
hth
