Sounds like you have done really great work, and have come a long way. Being able to have painfree PIV as times is amazing.
Something to consider might be diazepam suppositories to help further relax the muscles. They are a prescription and you would need to get them from your gyn.
Botox injections can also be helpful, as that would paralyze the muscle and make your PT and dilation even more effective.
Trigger point injections with a pain management provider might also be helpful, if you can really target the spot that is painful, a skilled provider can do an injection in that specific muscle to help relieve the pain.
The diazepam suppositories might be the easiest way to go first, try that for a month or two with your dilation and PT and see if you have more improvment.