What are my chances of winning a case against my ex-employer?

1) In your state (CA) , you are entitled to be paid (in your final check) for any accrued but unused vacation days, so you should be able to sue for this, or possibly file a complaint with the state's department of labor, who may be able to help you.
2) If you were not exempt from overtime (e.g. if you were hourly; or if salaried, if your job did not meet one of the tests to be considered exempt, such as the professional employee, administrative employee or executive employee tests, which you can find on the U.S Dept. of Labor website under "overtime") but were not paid it when working more than 40 yours per week, you may be entitled to back overtime for up to the last 2 years (assuming you can prove the hours you worked). Again, you can sue for this money or contact the state departmet of labor, which may be able to help.
3) Health insurance premiums: if they did not pay premiums while you worked there even though insurance was part of your compensation and you incurred out-of-pocket medical costs which you should not have, you could sue for those costs.
3a) However, they had no obligation to pay for your insurance after you quit, and you cannot sue for that.
4) Defamation: IF you were truly defamed, you could sue for compensation for it. But defamation is ONLY the making of untrue factual statemements about you to others, which statements harm your reputation. Examples:
a) Your former employer says you quit work--that is not defamation, because it is true.
b) Your former employer says you asked her for financial help for a personal problem (the wage garnishment)--that is not defamation, because it is true.
c) The former employer says that she considers you "ungrateful" or that you had become a "bad employee" towards the end or you let yourself be "distracted" by your domestic/personal issues--that is not  defamation, because those are all opinions (personal or subjective judgments, not provable facts) and opinions are not considered defamation, even if harmful.
d) But if your employer says you stole from her, or falsified time records, or were absent without using vacation days or were chronically late, if those things were false, they may well be defamation: untrue factual assertions. You could sue over statemets like these.
In regards to 1) and 2) contact the state department of labor: they may be able to help you for free. If they can't or won't, you can sue, and if you have to sue for those clear-cut things, you can in the same  suit also throw in 3) (if you are trying to recover medical costs you should not have paid) and 4) (if these are untrue factual statements being made about you)--i.e. if you have to sue, you should add in any claim you can add in good faith.
If you can't find an attorney to help but want to sue, you are allowed to sue as your own lawyer, or "pro se." You should be able to get instructions and possibly sample forms from the court (e.g. online, or at the clerk's office) and can look up court rules online.