You’re really caught between a rock and a hard place aren’t you? You’ll either upset your family if you un-ask her or you run the risk of her upsetting you both on the day and in the build up. My advice to you would be to tread carefully – don’t give her the reaction it seems she’s looking for. If she wants to use another hairdresser, let her. Book the rest of the bridal party in for their appointments and let her know you haven’t arranged something for her ‘as you understand she doesn’t like that hairdresser’ but be clear she’ll have to arrange her appointment on the morning and travel to and from. If she’s disrupting plans for the hen night, carry on regardless and just let her know the date and time that it’s going to be and say ‘we’ll be so upset if you can’t make it but this date was the best for the majority of people’. To be blunt, the wedding doesn’t revolve around her and this is a subtle way to remind her of that. You’re not being cruel, you’re not starting arguments, you’re just getting on with all the arrangements. If she feels she’s being left out of the planning completely, I don’t think she’ll like that at all and she might well be a bit more accommodating to avoid being shut out. But, if nothing changes, I think you might just have to accept the fact that all she’s going to do it turn up on the day and wear the dress. If that happens, try to swallow the hurt and enjoy your wedding day. You’re marrying the woman you love and no bridesmaid can ruin that. Good luck.

Isn't it funny that weddings can bring out the best but also the worst in people? Are the bridesmaids having the same style on the day? If not, then agree that your sister can go to her own salon but on the understanding that A) You will not pay B) she must be back with the bride and bridesmaids at X time. Reiterate that you & the bride are disappointed because you would have liked the bride and ALL bridesmaids to bond the morning of the wedding. You can also mention it doesn't give a good impression if the grooms sister doesn't want to spend time with the other girls. I know its emotional blackmail but sometimes that is the only way forward. If on the other hand all bridesmaids are having the same style then explain to your sister for continuity she must have her hair done at the hairdressers otherwise she will look like the odd one out; and the photos will look strange with one bridesmaids hair different to the others. Explain that it is really important that the 2 ladies that mean a lot to you will be united on the day and that it will make you proud seeing her walking down the aisle with your bride. Good luck and remember the only thing that matters in all of this is becoming husband and wife, don't let your sisters childishness spoil the day.