There is a 3 year statute of limitations for filing a contempt proceeding for failure to pay child support; however, you mentioned that you have a parenting agreement incorporated into a court order regarding the split of the medical costs. This does not fall under the 3 year statute of limitations, but the 12 year rule. The SA's office may be reluctant to pursue this since it is not direct child support. You should speak with an attorney regarding the possible pursuit of a breach of contract/enforcement action.
This is NOT legal advice, is GENERAL INFORMATION ONLY, and does NOT establish an Attorney/Client Relationship. Therefore my answer cannot address your specific legal situation and you should not rely upon my answer in your legal matter. I am an attorney licensed in Maryland.
There is no statute of limitations for child support in California.. Look at your order what does it say about medical expenses,
My name is Stephen R. Cohen and have practiced since 1974. I practice in Los Angeles and Orange County, CA. These answers do not create an attorney client relationship. My answers may offend I believe in telling the truth, I use common sense as well as the law. Other state's laws may differ.. There are a lot of really good attorneys on this site, I will do limited appearances which are preparation of court documents it is , less expensive. However generally I believe an attorney is better than none, but many will offer a free consultation and a face to face meeting generally will be better, I like my clients to write a short one page history of the fact and questions they have prior to meeting with them, so nothing is forgotten.
Statutes of limitation only prevent a lawsuit from being filed or it can be used as an affirmative defense. You already have a court order - so that takes precedent. However, to enforce a court order, you would need to file a petition for contempt if she has not complied with what the judge ordered, which you can still do.
This is not legal advice nor does it create an attorney-client relationship. This is for education and informational purposes only. It is always recommended that you contact an attorney with any concerns as each individual case is unique.