She has gained weight, 50 grams in the last 2 weeks (I forgot to weigh last week... oops) which I believe is normal at her age (4-5 months) and is around 650 grams. I can feel her spine and ribs a bit, so she doesn't seem to be overweight or anything (although she does weigh 50 grams more than her cagemate). Other stuff (eyes, energy, appetite, etc.) seems normal as well.
She is from a pet store (I know how bad they are now, but I didn't at the time) so she has never really had a good vet check-up or anything. Do I need to take her to a vet? She still seems to have cloudy urine.
Also: Lynx - I have looked at my piggie notes, and I haven't ever noticed cloudy urine after eating grass before. That is the only dietary change I can think of, apart from them having a couple snap peas (as a treat), which they have had before (also with no cloudy pee).
If it is only cloudy, not gritty, I would at this point primarily monitor her and pay attention to diet. Read over the stones page for links to dietary info.
The water isn't disappearing at such an alarming rate now (although still faster than normal, it seems) so hopefully it was just a weird thing.