Hi,

Of course you have the right to ask for someone that you feel comfortable with!
It's your birth.

I have never asked for someone different but when I was a student midwife, there was one midwife who nobody liked. One day, I was allocated her and she was really mean to the woman and her family, who were in birthing their forth baby. After a while, it was apparent that the midwife and the woman were not getting on and she asked for someone different. The midwife was upset that she had been asked to go (she was a senior core staff member in delivery suite) but it was just too bad, the woman (who was experienced and knew her stuff) was not going to put up with that kind of treatment at her birth! I was very happy to see her stand up for what she believed in!