Our kittie's revenge?

We've got Scirocco for about 3 1/2yrs and she has NEVER failed to use her
litter box. We had our annual trip to the vet Tues night & apparently grabbed
Scirocco with a full bladder 'cause she peed all over herself in the crate
on the way there. She got her exam & shots and a towel dry at the vets. When
we got home, my DH gave her a bath. So Scirocco really suffered a trio of
indignities all in one night.

Last night or possibly this morning she peed on DH's sweatshirt. (He keeps his clothes
in a pile in his office. She loves sleeping on that pile).

So... is this revenge & a one time deal or do we have a budding problem we
need to nip fast? Any experience or advice?

Thanks
Tam