There's no such thing as a cause of action for piracy, and no you can't sue for copyright infringement in Small Calims court. You also can't sue anyone for copyright infringement without at least applying for copyright registration for your song.
You solely wrote this musical composition, right? You own the copyright in the music and the lyrics, right? Have you registered your copyright? If not, why not?
Have you formed a music publishing company for ownership of the song with one of the performing rights organizations, ASCAP, BMI or SESAC? Have you registered yourself as a songwriter with one of the PROs? If not, why not? PROs are supposed to get paid every time a song is performed on radio, or TV or in a film or in a live show. Hint, hint. You can sic your PRO on this performer for not paying you while continuing to perform your song.
As for the YouTube video, yes, she needed a "synch" license from you in order to synch your song with her videoed performance. But she's not making any money on YouTube, and you're unlike to get the $150,000 damages per infringed work that could potentially be awarded in a copyright oinfringement case, even though this sounds like willful infringement.
Educate yourself (plase see the guide linked below), then do your registrations, and start treating your song as the valuable asset it is.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Federal questions are limited to federal jurisdiction. And in Small Claims in state court, you can't get the injunctive relief you need, either. You only get money.
But you might get the benefit of attorney's fees provisions in federal court, under the statute.
The facts of your question are inconsistent. Who worked for who? You say not only that you were employed by the other person but also that the other person was your former employee. Either you worked for the person or she worked for you -- or neither of you were employees of the other [which is most likely]. Settling this issue makes a difference when responding to your question.
My best guess is that the other person hired you -- via a written contract -- to write a song that she would then perform somehow. If that's the case, then when you wrote the song you were an independent contractor [neither of you were "employees" of the other].
If, as you say, the contract spelled out that you owned the copyright in the musical composition of the song [its words and music] then you do -- assuming all contract formalities were met.
The question then becomes what the contract says with regard to the scope of the license that you granted to the other person. You say that the license ended when you were "no longer employed by her." But you likely never were [being an independent contractor] so that statement does not help at all.
If you were, in fact, an "employee" of the other person when you wrote the song then there is a fair to middlin chance that even with the contract granting you copyright ownership in the song the other person has a PERPETUAL, non-exclusive license to perform the song.
Moreover, it is usually the law [if not always] that when a person lawfully makes use of a copyrighted work during the term of a license to use the work the person's creative results [in this case, apparently, a video] can be distributed and sold in perpetuity. The person cannot make a NEW work using the licensed material after the license expires but all the OLD, lawfully made works can still be reproduced, distributed and sold -- forever.
BEFORE you figure out if you have any sort of claim against the other person you need to figure out these fundamentals.
Sir, you may sue in small claims or state court but ONLY on the breach of contract claims. You cannot get copyright damages or an injunction based on your copyright if you sue in a state forum. Jurisdiction over copyright issues is a matter reserved to Federal Court jurisdiction.
There are two additional courses of action you can take.
1. Look for a local chapter of VALA--volunteer lawyers for the arts. When I lived in the Bay Area I volunteered with this group. They will do an intake interview and match you up with an interested attorney for pro bono service.
2. That said, if you cannot afford a copyright lawyer but want to pursue the copyright claim, please go to your local federal district court website and look up the special provisions for pro se complainants. You may find this information on the website or in the local rules. Many federal district courts are hiring pro se managers/clerks specifically to deal with the pro se case load. I know for certain that the Northern District has one (covers SF, Oakland, San Jose etc.) The Central District (LA) and Southern District (San Diego) of California may have one as well.
The court's main Clerk's Office (where you file your papers) may be of some help too, and Judges personal law clerks will likely spend a little more time figuring out your papers than they would those of a represented party. (I speak from experience as a former clerk).
You can go to a local law library (any law school) and look for Nimmer on Copyrights--it is a treatise on copyright law that will have sample complaints in it. Model yours on one of those. You can't check a book like that out of the library, but you can make a copy of any federal court pleadings that are included in the treatise--those pages are not copyrightable.
You will need to register your copyright before you file a complaint. Good luck.