I think you and your child should shy away from diagnosing anything - your daughter has decided she has a learning disability? But you cannot dismiss it either and "tell her to pay more attention." She's telling you that she is counting excessively and obsessively, and it's bothering her. If it's interfering with her life - and it sounds like it is - she could benefit from professional help. But you all need to get clear on definitions and diagnoses - a professional can help you with that. Encourage your daughter to describe her symptoms only, rather than suggest a diagnosis of "learning disability" or anything else.
I'm not sure the pediatrician can do anything. This doesn't sound like anything that's his/her specialty, although if there's a need to rule out other things, that might make some sense.
I think that this may well be a mental/emotional issue and that you should consult a good child or adolescent psychologist or psychiatrist. There are many behavioral techniques that can be used to lessen the obsession to count. A good friend's son has significant OCD tied in to Tourette's Syndrome, and he benefited from a pediatric neuropharmacologist as well as a behavioral psychologist. Medication was part of the treatment but not the only part. Adolescence was a very difficult time because changing hormone levels really messed with his brain. Your daughter may have this issue at 13.
My cousin has significant OCD but unrelated to a medical condition. In his case, therapy is the indicated option. Any psychologist will have a relationship with a physician (psychiatrist) who can prescribe meds if indicated, so don't worry too much about an MD vs. a Ph.D. It's more important to get someone your daughter can related to. Be prepared that she may resist this - it's important for her to understand that she is not crazy or making this up, and she can't just snap out of it or pay more attention so it goes away.
She's giving you very clear signals that she needs help. Reassure her that she did the right thing by telling you and that, together, you will work to get answers.
If you need a referral to a psychologist, you can start with either your child's doctor or your own, or talk to the school psychologist about someone who takes your insurance coverage.