Question about kitten behavior

About 6 weeks ago we got a 15 week old kitten, Roxie, to add to our family,
which includes a 7 year old cat, Trixie, and a 6 year old dog, Dawson.
Roxie fit in great and rapidly became friends with our dog, although she has
a strained relationship with our cat as we expected. Both our cats live
indoors and share a litter box.

Anyway, to the problem. About 3 weeks after her arrival we were just
getting to sleep when Roxie walks onto the middle of our bed and pees on our
down comforter. We didn't know what to make of that, maybe her litter box
was a little dirty for her taste and she wanted to clue us in??? We left it
at that thinking it was a one time occurrence. She's never peed anywhere
else besides her litter box (that we know of). So last night, we finally
got around to putting our freshly dry cleaned comforter back on the bed when
the same thing happened. In the middle of the night, Roxie walked across
the bed and peed on it. This time I know it wasn't because her litter box
was dirty, so obviously she's trying to tell us something. But what?
Anyone seen this type of behavior? Could she be marking her territory or
could it have something to do with the down? Any ideas on what this is or
how to fix it would be great. TIA.