Has got a lot worse. I think its got an ulcerated scab on it. I sent a gross photo of it to Guinea Pig Rescue Lady. Her advice was to stop grass time and keep her on fleece and give her a bath to remove dried on urine. Millie just sits in one place now, even when out in the run. By the end of the day she is sitting on a poo mountain.
This very sad as Millie loves her run. I'm going to partially follow advice. Still put her in the garden but for short periods of time and not give her any tunnels to encourage her to move about.
For the first time ever Millie enjoyed a bath. The water supported her lump and fluid retention which must weigh a fair bit.
The scabby bit seems sore so I give her some Metacam, which she took greedily.
We are about to go away for another skating competition. DD1 will be charge of Millie. We have enough Metacam to last until we return.
Not sure what the vet can do apart from prescribe more Metacam. The opinion was that lump can't be removed last time we spoke. I doubt the scab will ever heal :(