yet another spider ID request

I live in the Pacific Northwest US, near BC Canada.

I cannot get a decent picture of this spider, damnit. :(

She's black, very shiny, in the way a black widow appears. She has a very
round abdomen and long hairless black legs. She does indeed look like a
black widow.

On her back are two light tan or dirty yellow colored spots, semi-pointed,
semi-rounded. Her body is just barely bigger than a common housefly.

She's doing a fabulous job of killing flies in our windowsill, so I don't
want to disturb her.

I am pretty sure she's not a black widow, because she has markings on her
back. I cannot see her belly to check for the telltale hourglass, but I
don't think its necessary.

tia!
fr0glet