This month has been particularly sad for guinea pig owners . Regretably you can not put your gp with bun. Rabbits can inflict terrible injuries on guinea pigs. And they are not really company, they don't speak the same language. Its like housing us with chimps and expecting us all to get along because we are all apes.
Rather than starting again with a baby. How about getting a new companion the same age from a rescue.
((Hugs to you and your DD)) losing a much loved pet is dreadful .
I'd leave them as they are. If they can see each other, that's company enough. Mine live in the same room (at the moment, although GP's are moving elsewhere in the house soon) and Current bun (only bunny) seems to find the GP's annoying. They do run round together for at least an hour a day, but this is not something all rabbits could do as they can inflict a lot of damage on a pig. Luckily ours is a wuss and scared of the GP's and they get on okay, so I don't supervise them full time now whilst they're together.
Your rabbit sounds fine on his own. I would focus on giving your GP extra cuddles etc whilst she adjusts to being on her own. Lots of parsley should help!
My GP's regularly eat from each others bowls - they're not supposed to, but they sneak a bite when they think no-one's spotted them sneaking in his cage. The main problem I would have with the bunny and pigs together would be the veg. Current bun only likes carrots and cabbage whereas pigs like everything - there'd be a huge mess of food all over the cage and bun would be cross as he's tidy.