Some Rabbits cope better with bereavement if all reminders of their deceased partner are removed. Things that may smell of him
Introducing some new and hopefully interesting toys can help too.
This approach is certainly not suitable for all Rabbits, but I know for a fact that it can help some who become depressed due to bereavement.
For example Lady Lydia, who has grieved for Sir Victor more than I could ever have imagined
, has improved considerably in a totally new enclosure in a different part of the house. Even now, over a year after we lost Victor, Lydia becomes depressed if I put her out into the garden she spent so much time in with her soul mate. She will not, under any circumstances, go anywhere near the area they used as their latrine. She has also made it abundantly clear that she will not tolerate sharing her space with another Rabbit.
At the other end of the spectrum I have known Rabbits who appear to be not in the least bit bothered by the loss of a partner. In fact a few appear to become much more active and interested in things.
Both grief reactions are equally agonising to witness
Maybe you could get Dana checked over by the Vet again, just to be sure that her demeanour is not due to a worsening of her health problems.