My first concern is that two adults are permitting a 6 year old to run the visitation show -- she refused to come with you and you didn't insist? Nor did your ex insist?
I'm from Virginia and don't recall that there is any type of law regarding taking a child for counseling that requires 2 signatures. How about trying another counselor? How about taking her on your time?
As for her mom not picking up the phone when the child is with you? Not much you can do about that one, Mom's entitled to have a life also -- if you're staying home when the child isn't with you just in case she calls? Good for you. Mom isn't. Mom didn't pick up the phone, the child asks you to drive her to mom's house and you DO IT????? Who's the adult here?
How about distracting your child, involving yourself with playing a game, seeing a movie, etc and leaving her mother alone during your parenting time? You're setting a bad precendent here for not being able to care for your own child and permitting her to call the shots as it comes to parenting time.
Your divorce and visitation provisions are reasonably new....your child WILL get accustomed to it.....when you take her back to her mom's or go looking for her mom because she didn't answer a phone, you yourself are validating the child's fears that this isn't a good situation.
It's up to both parents to make this work. BOTH parents. If, after a period of time, with positive interactions with both parents, your daughter still has a huge anxiety issue? Then I think counseling might be in order. At this point in time though, you're fueling her anxiety by doing things like letting her freak out about her mom's whereabouts....
Is mom doing the same thing? Driving her over to you if you don't answer the phone? Or is she somehow reassuring this child that daddy's out doing something and she can talk to him tomorrow?
You're very willing to take things into court that will probably work themselves out given time -- time that you're not letting it take. There's nothing instant about life as a divorced family, either for the adults or the children but children need to have faith that the adults in their lives will always do the best for them.
Letting a 6 year old **refuse** to go with her father? The PARENTS are the biggest part of this issue.