I've been in business for myself, and I've also done accounting for independant lawyers, so I have lots of experience trying to collect debt from clients.
You should send a reminder notice to her. Be polite but professional. Something along the lines of:
"Our records indicate that you have an outstanding balance for your account in the amount of <insert dollar amount here>.
If payment has been recently remitted and not received by us, please accept our thanks. If not, prompt payment of your account would be appreciated.
To report your recent payment, please contact me at <insert phone number here>.
Then give her another 2 weeks. If that doesn't work, then send out a second notice, something along the lines of:
"Further to our reminder of <insert date here>, our records still indicate that you have an outstanding balance for your account in the amount of <insert dollar amount here>.
Kindly remit payment immediately.
Give her another 2 weeks, and if that doesn't work, send her something along the following:
"Despite our reminders to you about your outsanding account, we have not received payment.
Unless payment is received by <insert date here> (give 10 days), we will be forced to take further action against you without further notice.
However, if you send something like that and she still doesn't pay, be prepared to follow through with the threat, either through a collection agency to assist in collecting the debt, or have your lawyer send her a legal letter.
If the legal letter doesn't work, you may have to resort to small claims court to collect, or chaulk it off as a loss and claim that loss on your income tax (here in Canada you can do that, not sure about US though)
Either way if she is a problem client when it comes to paying, perhaps you shouldn't do any further work for her? Or you should be getting 50% down prior to starting any work for her.
This post brought back a funny memory for me. Indulge me for a moment...
I used to work of a restaurant supply company that sold and serviced a wide range of restaurant equipment including slurpee machines and freezers etc. My job including secretarial was also accounts receivable. There was a client that was a COD client because they had been known to not pay their bills, and one of the servicemen who went to do service for that restaurant forgot to collect the service fee.
I tried for weeks and weeks to collect. Finally after about 4 months of getting no where, I called the manager of the restaurant and told him that I would be there at 5:15 pm to collect the fee. I told my boss that I was going to go there and get the fee after work.
I took the bus at that time, but the place was sort of in the vicinity of where I lived so I just took an alternate bus route.
I arrived there and the manager/owner gave me some song and dance and wouldn't pay me.
I pulled a chair out from the dining area and placed it right in front of his cash register and sat there!!!!! It was a great inconvenience to his customers, especially when I said that I was sitting there waiting for the owner to pay a bill that he owed my company.
He held out about 45 minutes, but then he tried to give me a cheque. I told him I wanted cash (I didn't trust that his cheque wouldn't bounce). I got cash and on Monday morning I went to work and presented my boss with the envelope of money. They were rather impressed.
One of the sales guys attended Dale Carnegie courses
and he told the story at one of the seminars. They were quite impressed and said that I didn't have any problem at all with being assertive, LOL
Anyway, I do hope you get your money. It's hard when you are self employed and end up with deadbeat customers. I've had more than my share of those with my graphics and web building. Unfortunately it's much harder to collect debt when it involves cross country/province/state transactions and never having met the person face to face other than through message programs or via telephone.