I would let sleeping dogs lie. Buy a Certificate of Deposit in both peoples' names. Since you gave her the engagement ring (presuming here it was a set) before marriage, that's her separate property anyway. The wedding ring itself is community property, so it's appropriate that the dollar-value be shared.
If you reconcile, celebrate with a new ring.
If you don't, split the money and buy some whisky.
Did she, as Mrs. SP did, have a "sport band" -- that is, a plain band worn for activities where diamonds were inappropriate? If she does and wants, that could be a "place-holder."
Alternatively, and no endorsement here is express or implied beyond what is written -- I have no financial interest here -- the John Christian jewelry company does a nice "Mother's Ring" (I bought one for WAW before I deployed to Iraq years ago), and I noticed the other day that WAW is wearing it in lieu of a wedding ring.
So you could go that route -- symbolic of the family, her motherhood, etc. -- without treading into "are we married or divorced or what?" territory.
