If this lady rings back to make an appointment, I will stipulate that payment is required up front. I have also ordered new brochures advising that payment is by cash or cheque only on day of treatment.

Think I'd say "at time of treatment". Otherwise you could be in the same situation again.
Marion x

Send the woman a polite letter by recorded post, if she doesnt reply/bring the money ring your local trading standards and see what they say. good luck

I am sorry and I don't want to sound mean here, but, what on earth made you let her leave without paying? You should have said I need to hold your drivers license or a credit card. Something! If she had nothing to leave as collateral you might have said .. You will have to sign this receipt of service stating you still owe $$ and sign it both of you, date it and add the time of service...
Now enough with the shoulda coulda woulda since it wont help here, write a letter of neglect to pay on a service with a reminder of the fee, the date and time she was in. State in the letter how many days she has from the day you SEND the letter until you expect payment in your hand. 7 days is OK. Include a consequence if payment is not made by then.... Like you will then proceed with legal paper work to go to small claims court, where you will be forced to sue for the appointment time AND court cost.
Its hard in these situations but, Things like this will only go where you allow them to. So be strict and on top of it, so she and those around you KNOW this is your business and how you make a living. You are proud of it, and you take it seriously.. If you allow her to get away with it, just think of the way she will remember you. Like a push over.
So Be it.... Get that money!

OK only now that I have submitted my reply did I see how many pages this post goes for... I see that you got payment... GOOD.
I also see that she said she forgot....... How may I ask do you forget to make a payment for a service after you can clearly see the results every hour of the day? Not to mention you said yourself you had to put ANOTHER reminder under the door. OK I am sorry but that is rediculous.
Now I read that she is making another appointment! What is going on here. Not in this life time would I EVER re-book a new client who "forgot" to pay even after a reminder let alone one who IGNORED my attempts to make contact and figure out why she didnt pay.
In this case like I said before Things Happen that YOU allow. So take on a client who is unreliable and you will reap the horrors of that. She has shown how much she respects you already. So if you like having clients who are rude, late, forget you, dont show up, expect you to go above and beyond all the time, well then thats what you will get.
I would have made sure to say that based on recent events you feel she is not a good match with you as her nail care provider. Period.

I cant see where pippadoodle said this lady HAD re-booked...???