GET A LAWYER. IT IS NOT TOO LATE.
It doesn't matter whether or not your sister "dropped" the charges. The State still proceeds. A nolo plea goes down on your record exactly as a conviction, so that doesn't help you at all.
If you have waited until the trial date to ask for an appointed attorney, the judge will very likely deny your request.
Please let me know if I can be of assistance. I would be happy to help.
M. Jason Rhoades
It sounds like you waited a bit long to start on this issue. In the future just remember earlier is better.
In short, you can take whatever "plea" is available to you at the time of trial, but also remember that the State may have been having a problem getting the necessary "witnesses" to effectively prosecute you, so the State may have a hard time actually convicting you. I would go get an attorney, and fast. Hopefully that will buy you the time and/or analysis you need to prevent ending up holding the short end of the stick.
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If you cannot afford Counsel Counsel may be appointed to represent you.
You should consult an Attorney that handles Traffic cases in the jurisdiction you received the citation to evaluate your options.