I think you should make sure M takes her, to the point of carefully consulting diaries! She will almost certainly be picking up subconsciously from you, in some way, otherwise she would display the same behaviour with Mick!
When I was still phobic, when B and H were little, their dad always took them! He has never minded the dentist, and I really did not want them picking up my fears.....neither of them minds going one single bit