DH and DD got two 8 week old female rabbits (sisters) just under 2 weeks ago, we got a phone call from the pet shop after a week asking us to take them in to be checked by a vet as there had been a problem with some other rabbits. They were checked and deemed to be fine.
One of them has died today. 
I know rabbits are happier in small groups but the pet shop have said that if we get another female rabbit they could fight as they will not be used to each other.
I don't like the sound of that but don't want the remaining one to be lonely either.
What shall we do?