I.G.
I think that in this situation trying to make it "special" will only backfire and mom will feel even more rejected if her daughter is not appreciative after she went through a lot of trouble in "making it special".
They should just tell her matter of factly.
When my sis's youngest came along her oldest daughter was 10. She was NOT happy. She was not happy about any of her sibs. She gets along "soso" with most of them, she knows not to be disrespectful to her sibs and she will watch them when asked to... but she would never volunteer and she prefers to spend her time not being bugged by them (she is 14 now).
I think that's ok too. I mean we don't get to choose whether to have sibs or not and as long as she is respectful, it's ok not to be all googoogaga about a new baby.
For my niece... she is still young, but I would not be surprised if she chose to remain childless as an adult... little kids is just not "her thing".
I would advise your friend to just keep her expectations in check and who knows... maybe her daughter will come around and be excited eventually.
Good luck.