DSD (14 yrs old) came to live with us permanently (from over 60 miles away so had to change schools). As we are Catholics, DSD was enrolled in the local Catholic Secondary School. DSD became upset that her new school friends thought it was unusual to live with a step-mother and that I must be like the one in "Cinderella" - the 'wicked step-mother'. It was unusual because divorce and re-marriage was not accepted by the church in those days.
So after 2 months, I said she could a group of 8 school friends over for tea and playing on a Friday to meet the family. (There was no internet at this time.)
She made her list, then added others because 'I can't have A without B because they are good friends'. She started crossing off her chosen friends to try to keep groups together. Anyway, we extended it to her having 12 friends in total because I was impressed by her thoughtfulness. She then asked if she had to have a neighbour's 2 DDs. I asked, "Would you like to?" I also said that I wouldn't count them in her 12 guests. She didn't want them to come because (allegedly) they had bullied her for 3 years about living in an area that was quite deprived. [I have to say here that DH paid more than the expected amount for his DCs. She had her own clothes at our house - we had her for all holidays previously.]
The party evening was great - lots of fun and laughter. We met the parents on drop-off/walking round of the girls, so it gave us all a way to meet when DSD hadn't come through the usual primary school to secondary school system. We recognised most parents from Sunday Mass - so we became included in the parental group that 'hung around chatting after Mass' whilst the girls caught up in a corner of the car park!
Anyway - back to the party ...... The next day I was challenged in my own home by the neighbour/friend. Because my DSD had always played with her 2 DDs since she had spent holiday time with us, she thought her DDs should have been invited also.
I explained that it was a school-friendship party, not a regular party. Her DDs went to the non-faith secondary school, so weren't part of the school-friendship-family-introduction-party. It was a chance for DSD's friends to meet 'the new family' in the school. It was also a chance for the parents to walk their girls to our house and meet us as they 'dropped off/walked round'. It had a specific purpose.
I counter-acted with the times when she had family parties for her DDs. I absolutely understood (as did DSD) that there were times when family social occasions are for family only.
My neighbour/friend and I managed to fix it at that point in time but became too hard to manage long term.
Can I leave you with one last thought:
I was widowed (aged 46 yrs - no birth children) so please enjoy your children and don't find a chance to fall out with other Mums. Bring up your DD to be sensitive and caring and then able to put on her 'big girl pants'. Be light-hearted and up-beat about how friendship groups change. Save your lioness for when it is needed.
Not every situation needs conflict or challenge. I wish I had been wiser when I was 28 years old bringing up a DSD aged 14 yrs old.