If you have all of these emails I would print everything off and make a visit to her house to discuss in person. If she refuses talk to a collection agency, yes you won't get all your money because they take a cut but still usually cheaper then hiring a lawyer or going to court over it.
I had one client owe me $350 for final clean up and cutting. I showed up at his door Monday morning 6am and parked truck and trailer in front of his driveway and just waited for him to try and leave for work, because he wouldn't return any of my calls. Gave him all the paper work of his approval for work and told him I would be here at 5 to collect CASH! He wasn't happy but I got my money!
Truck, Mower, Trimmer, Blower.....same as everyone else.