I would only be concerned if it kept getting bigger. As long as it stays that small it should not be a big problem especially now she is spayed and is not at risk for a pregnancy making the hole stretch more.
Try to keep her fit not fat so that the fat won't be pressing on the small opening either.
But if it enlarges you might want your vet to repair it.
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics