I now see this is a continuing issue since you began the care of this animal for your sister.
http://ball-pythons.net/forums/showt...er-my-bathroom!

Read up on diamond pythons in the links I posted.

I think in a very short time you will need to visit a reptile vet as it seems the health of this animal has taken a dive since you started helping out.

Find out how the snake was doing prior to you taking it in as the issues could have started while not in your care.

If the snake was perfectly fine, you need to do EXACTLY what was being done before you took it in, however in order to know things were good, you must find out if your sister changed anything with the care of the snake recently as well.

Diamonds are considered "cold weather pythons" though cold is a relative term here.

THE COMPLETE CARPET PYTHON By Nick Mutton and Justin Julander has a separate chapter for the care of diamond pythons.

You may want to buy the book and study that section.

Unfortunately I don't own a pure diamond so I'm not able to pass on anything more than I have.

Good luck.