Please take her to the vet to have her checked out - I've just posted an RIP to my Lady G who died on Sunday, had also lost weight, watery droppings, not laying, also used to stand off from the others looking "down" but would perk up when I called her. I also fed her on bio yog mixed with mash & some grated cheddar (watch your fingers though, they love cheese!). Check out her undercarriage to see if there's any swelling, but please, whatever you do, don't make the same mistake I did and leave it too late to get help, you'll only regret it!