As a general principle, a contract in the U.S. merely requires an offer, an acceptance, and consideration; a contract does not have to be in writing to be to be enforceable. Writings are preferable because they are more easily provable. It is not the lack of a writing that would likely be troublesome for you here, but the lack of concrete terms, i.e., what exactly have the two of you agreed to?
Additionally, I believe you said that her bank informs her before cashing her checks, which would seem to be a serious violation of any bank's policies (I put myself through undergraduate school working in banks, and this never, ever happened). If banks informed account holders before cashing their checks, virtually no judgment/lienholder or other creditor would ever be able to collect what they are owed since the account holder would likely do what you fear your debtor has done here--simply write worthless checks and then clear out their accounts before anyone could collect.
I think Ellie Mae has given you the best advice on maximizing your chances of collecting in the worst case scenario (i.e., if you cannot simply cash the check and remit the overage to your buyer by bank check via registered mail--you definitely want to cross all your t's and dot all your i's with this woman)--contacting the DA in both her and your own jurisdictions, describing your situation and asking for advice on how best to handle the situation.
Additionally, you generally do not need an attorney in small claims court; it can't hurt to get legal advice if it makes you more comfortable, but you should not need legal counsel to pursue such a claim. You just want to make sure this doesn't end up costing you more money than you can ultimately collect from the legal action. Good luck with this!
