Admiration for foster parents

I think I've mentioned my coworker who has taken in her 5-year-old
grand-niece (great-niece?).  She brought the kid in today on her way to
some other appointment and we said hi to the child.  The girl spent most
of the five minutes standing behind my coworker, hitting her on the
back, and saying "Old lady! Old lady!" over and over.  My coworker
seemed unfazed.  My inclination would have been to grab the kid's arm
and say "knock it off, you worthless little ****", and this is why I
have been so very careful with birth control all these years.  

My stepson acted up sometimes but somehow he was comprehensible to
me, maybe because he's very like his father, so even when he was being a
little butthead I could sort of understand and work with him. 

But a kid like this girl who has spent her whole little life with a
bipolar drug-addicted mother or in foster homes?  How could you ever
deal with that?  

And where do people learn all those clever, soft responses to children
who are being awful?  You couldn't just tell this kid that that was a
mean thing to say and she should stop it, because I think she just
would've gotten more into it. 

Have any of you ever been foster parents?  Could it possibly be worth
the pain? 

-- 
Dover