I think 9 days is not unheard of, but it could be that there is something else going on.
I had a mare in for breeding once that was receptive to the stallion for over 30 days. It was early in the year and a transition kind of thing is what most of the people I spoke with said. She finally did take on the heat following that one, which was at the end of May. The other went from the first week of April all the way through the first week of May.
I don't know all of the reasons that this happens, but you might want to consult with a local vet or equine reproduction specialist.
Liz M.