Thankyou so much for answering and I realise it was a foolish thing to do without experience.
It was neutral territory, none of them has been in the run since over a year ago when she was in there from time to time with her mum and sister, so I thought it would be alright, and it was alright for the first while - they looked happy, cuddled up together in a group after some initial chasing and tail sniffing.
I should not have gone out at that point. She was always the most submissive of her own group so I didn't anticipate she would fight at all, but the boys haven't been neutered yet and maybe that ought to have been done first.
I did clean her vent with cotton buds and water, very gently and got out the dirt. She was quite upset for a while that night, poor love. I felt terrible.
She's not overweight at all, her family never ate the hay I gave them or indeed grass (very strange) but they had, and she still has, rabbit food every day and usually fresh greens, sometimes a carrot. And I still give hay though she seems to use it more as bedding.
The girls were all in a huge walk in run last year but then managed to burrow out of it into the garden, which is when the fox took two of them. I have been unable to make it safe since as I know she will just burrow out again, so she has been in the hutch (6x2, not teeny) all winter since it happened and I was hoping she could share the run with the lads. We only got them to keep her company but they are in a separate hutch as I was unsure how to introduce them.
If you have any hints on how to go about putting them together properly, I would be really grateful, but if it's just not a good idea I will keep them separately. I did read up about it quite a bit before trying it, but obviously got it wrong.
Thanks again for all your help.