by all means get kitty checked out, but although it is unusual it is not unheard of for cats to eat odd things, like dirt or litter
my sisters cat just adores dirt! she won't touch a house plant, but she will dine on the potting soil if you dont' cover it well!
and i have heard of other cats that do this also
if you use the clumping cat litter, this may be dangerous- so you will want to ask your vet what to do
obviously you can't allow the cat to eat the litter, but you do have to use something for her to use as her bathroom....thats a tricky situation, i wish you luck!