Can she try to contest an uncontested divorce in other words?
Child Support Lawyer
A lawyer's favorite answer is it depends. An agreement signed by the Court is an Order, but an Order can always be reviewed, barring language that prhibits same. Without more detail, this is the best I can do. Good luck to you!
Family Law Attorney
If your agreement is turned into a Jud gent, you are done with your case and it is unlikely she can change anything other than the following exceptions:
You can always attempt to modify child custody, visitation, and support if there is a change in circumstances and the bes interests of the children are at issue.
Divorce / Separation Lawyer
I am an Illinois attorney and cannot answer your question authoritatively because it involves CA law. If it were proper to answer your question under Illinois law, then your wife would be allowed to change her mind in the circumstances you describe because her uncontested divorce "agreement" is not binding until the judge says it is. Until then, nothing of this nature is official.
Please check with a divorce attorney in CA to see if this is also true in your jurisdiction.