similar sit =- dd1 refuses to see ex, dd2 10 only infrequently.
we have been to family therapy which has been useful - please go to GP and ask for referral. this will also show courts that you taking your dd distress seriously and looking for solution.
I had to go with ex for initial assessment then attended sessions both with dds and them without me. and me without them. they used various techniques to draw out what was going on , what they wished from dad to make contact ok, etc etc. the upshot after few months is that dd1 resolute in no contact and dd2 only wants infrequent.
this doesn't stop dad demanding more but if they wont go; it wont happen. therapists who observed will also feed back to him...what it did do was make it clear the reasons why they want no or infrequent contact. and I see them as valid...I was also able to make clear I wasn't stopping them having contact, indeed was encouraging them.
what came out clearly was while there could be things he could do (or not do) to make contact better - they didn't trust him to do (or not do) those things.
if your dd is able to express in safe setting and with trained therapist what she dislikes about contact, what could make it better and whether there is possibility that dad would listen then over some months things may resolve - or may be clearer that contact is not in her best interest.
if she distressed at contact you can argue in court this is "reasonable excuse" for her not to go - if you proactive in asking for help with dd then cafcass/court will see you are dong the right thing t try to resolve the situation.