Such a sad story op but I think you are very brave, and honest, to share it. I very much doubt poor Edward is alone in his experience either. At least you did care for him physically.
There is a statistic I've read somewhere -can't remember where - that 90% of DC lose interest in a new pet within the first 8 weeks, so your DD was actually pretty typical, sadly.
I think there are two things that any prospective 'what small furry shall we get for the DCs?' reader should take from your thread.
- What do you, the adult (and especially the main carer) want? Do you actually like/love small furries yourself, or will caring for them quickly become a chore? Only ever get what you yourself want.
- With guineas, if possible, house them inside at least some if not all of the time. They become more sociable, much easier to pay them attention even if the DC aren't cuddling them, and much easier to organise feeding and cleaning out in the comfort of the house.
We have three DC and four guineas and our children have been very similar to your DD, if I'm honest. I do the care, and all the spoiling and cuddling too. And from time to time they enthuse about other animals they would 'love' to have (ooh mummy can we have a puppy, a kitten, a parrot, a terrapin, a bearded dragon) and I always always always say no. No, no, no. No, because, no matter what you would 'really love', I don't want one.
Guineas we have, because I bloody love them, they bring me a huge amount of joy and I will probably continue to have guineas long after I've got rid of the kids 
But nothing else, because I'm not prepared to love and look after anything else.
So yes, only get pets when you, the adult, really really want them.
RIP Edward 