I'm afraid I have some bad news about Harriet.
Yesterday morning when I got the budgies up, I noticed that she wasn't able to use her right foot. (The picture attached was taken before she lost the use of her foot.) I thought that maybe she and Pippa had had a fight, or that she had injured it in some way, so I toweled her and gave her some of Pippa's leftover pain meds and looked at her foot. There wasn't any visible sign of injury, but she was definitely unable to move her toes. By an unbelievable stroke of luck, my vet had an opening at 2pm, so I took Harriet in to get looked at.
Unfortunately, the prognosis is not good. The vet found a significant amount of bruising in Harriet's abdomen, indicating that she likely has some kind of organ dysfunction that is resulting in pressure being put on the nerves that control her right foot. The most likely causes, according to the vet, are either kidney cancer or reproductive disease. Because budgies are so small, and because of Harriet's age (she's 9) and relative fragility (since she's already had surgery for reproductive issues), the vet isn't confident she would survive the major surgery required to determine the problem, and the odds are there wouldn't be an effective treatment anyway.
So the decision has been made to try to keep Harriet comfortable with anti-inflammatory pain meds and in a hospital cage until her quality of life declines enough that it will be kindest to euthanize her. She is still allowed out with the other budgies, so she's not totally isolated, and as of this morning she is still eating well, destroying toys, and being very active and vocal (her wonky foot doesn't slow her down at all!), so right now she's doing well. She has already outlived all my other past budgies by three years (!!!), so although of course I will be heartbroken to say goodbye to this little fierce warrior, I am grateful for whatever time we have left.