I have both OCD and Asperger's Syndrome (Sensory Integration Disorder, or SID, is part and parcel of Asperger's), and my OCD started around age 3 (became severe at age 11 1/2), so I can sympathize with your plight. OCD is all about fear and doing things until they "feel right." Sensory issues are all about sensitivity to things that most people find normal (such as tactile sensitivity to shirt tags). The tricky thing with knowing whether it's SID or OCD in young children is that some children with SID may wash their hands a lot or check a lot, in order to rid themselves of the sensory issue. But with OCD, it's all about fear/feeling "right"/preventing something "bad" from happening. For instance, in SID, a child may wash their hands over and over again, because they hate the feeling of them being messy; in OCD, they may wash them to prevent somebody from dying of a disease or something of that nature.
In your granddaughter's case, the symptoms that will need to be analyzed are ones such as the tags in her clothes: Is she upset because they need to "feel right," in order to prevent something bad from happening? Or do they need to "feel right" simply because she has tactile sensitivity, and the feeling of the tag makes her highly uncomfortable? Your granddaughter's counting, in my opinion, sounds like straight OCD, as counting is not usually associated with SID. I have always had horrible tactile sensory issues, ever since I was a baby. My OCD always took a clear-cut "pure obsessional" form, even as a preschooler, so there was never any suspicion of overlap between my two disorders. However, I wasn't diagnosed with either OCD or AS until adulthood. AS simply wasn't known about during my childhood, and my type of OCD isn't as well known as other subtypes, so it was never suspected. Good luck, and if you have any questions, feel free to ask!
-GatsbyLuvr1920-