When you talked with her on the phone -- did you ask about payment? When she said she was very busy I definitely would have said something along the lines of "I understand you're very busy -- I just need to collect your remaining balance. Would you like to put that on a credit card and we can take care of this right now over the phone?"
You deserve to get paid. I'll be changing the wording on our Proposals and adding more fine print for next year. And that fine print will include something to the effect of 'if final payment is not received wihtin 5 days of install, the lights will be removed and you will lose your deposit.' It will sound better than that, but you get the idea.
BTW --- do you have a signed Proposal or Contract?