Jeff, are you her dad?
If so, one fact you will have to face up to is that you can't be her chaperone for much longer. If she needs support because of special need(s) you need to be putting in place the right groups and organisations to support her as an adult with these needs.
Is it that you are reluctant to let go - please consider this however painful it may be, because it may be that you are part of the problem, not the provider of the solution.
If you are her dad you will not be around for ever and she has to lead her own life and make her own choices.
My mother considered my bloke highly inappropriate and would have prevented our getting together if she could have done - we have been together for 29 years.
Parents can get it wrong. If the little bird can fly at all let her go when she's ready.