This is a really difficult one, and always hard for the cats - who are used to a hierarchy. I got No.1 Son as a kitten - so he is my baby (although now 11) and he and his siblings were always anxious and he still is. A female kitten then moved in and they got on well. Stray Rover (slightly older male) then joined us - all 3 were tabbies - all was fairly OK until the female got run over then No 1 started to really resent Rover. Black Spot later moved in from next door but he doesn't really care about anything, he knows he's a cat. However, years on, we still have constant problems between the two big tabbies - No1 Son always runs away and swears and hides, he just hates Rover even being. Rover is a gem and a funny cat but he will chase at every opportunity. Like these, each of them on their own is lovely!
I'm afraid it's a case of security for your first cat - she was there first and as a female may naturally be more timid, and the others are real threats to her in her own home. Introducing a new adult cat is always a risk - if I were your daughter I would have a word with the vet, Feliway may help the cats' tension.
I am however really sad to see that the unhappy cat has been declawed - I think this is a dreadful thing to do. Some people do it to save their furniture but it means that puss has no way at all to defend herself, or to catch things running past her - personally I'd never do it unless there was some medical reason.
I do hope this helps - I know all too well what it's like living with a bunch of disputing felines.