I'd say it depends on how much she owes you. Cos you'll need to pay for a lawyer to represent you so only you can figure out if it would be worth it to go to court. If it were me, I would terminate immediately for non payment of fees. Don't give her anymore chances! With people like that, you might not get your money even if you took them to court.

I can't believe you've watched her two kids for this long for free, basically. She's disrespecting you and you're allowing her to continue to disrespect you.