Brooke Mueller Takes a $20,000 Hit

1/25/2011 4:45 PM PST

Brooke Mueller Takes a $20,000 Hit

Charlie Sheen's baby mama Brooke Mueller has had a lot to do lately ... what with her reality show, rehab and stuff like that ... but now it's going to cost her $20,000.

Turns out Mueller didn't respond to a lawsuit claiming she stiffed a P.R. firm -- Rogers & Cowan -- to the tune of $20,142.91.

There's a legal maxim -- you snooze, you lose.   Hope she slept well, because the judge entered a default judgment for the full amount.

Attempts to reach Brooke were unsuccessful.