Using Arm 'n Hammer, Multi-Cat clumping litter.

Have three cats.  One of the cats, when she pees,
causes the litter to become a gooey mess, which
breaks up upon being scooped and worse yet, sticks
to the scooper and sides of the box.  (This is the problem
that defeated my Omega Box.)   Pee from the other two
cats is no problem.  The litter clumps firmly and is easily
disposed of, sticking to nothing.

Ideas?   I am starting to think either the one cat has
some chemical in its urine, or the same cat just
overwhelms the litter's clumping ability, due to shear
quantity of urine.