Well, my daughter has been begging me for a pug. I think they are precious.
Now, you can handle this situation 1 of 2 ways. 1st, the next time mom wants you to do her dog, tell her up front...it takes 2 hours to do him, either pay XXX amount or fill up my gas tank.
OOOOOOR, you can think of it this way...you're mother spent 18 +/- years raising you, giving you everything you've ever needed (at least the necessities). Do you really want her to pay for these services?
When my mom asks me to do her malt, Lily, I never expect a payment. It's the least that I can do after all she's done for me.