Aw poor Willow, hope the injections work, and the new tablets are easier, they certainly sound better if they are smaller, so should be easier to hide
If you're concerned about her weight at the moment, I'd also try cat milk, as well as dry food as well, as she's clearly drinking, so dehydration shouldn't become an issue? This is what I did with Max to try and build him up again, and it didn't make a huge amount of difference to his bloods.
Weird that she's liking sinks and showers at the moment though! Could it be that they are cool and it feels nice maybe? xxxx