No a durable power of attorney ceases to be effective at the time of his death. However, that may not have stopped her from transferring things before he died.
You will have to file a Petition to be appointed Administrator of his estate and then go out and investigate what happened to his property. She has little or no standing in the matter.
I practice in NY so check with a CA lawyer.
The power of attorney died with your uncle. ("Durable" means it is still good after incapacity, but not after death.) The poa would not replace the Will unless the agent under the poa diverted all the assets to herself before your uncle died. Then there would be no assets to pass under the Will. I know of one case where the agent conveyed all the property to himself after the principal died, without disclosing that the principal had died. Unless some interested party (relative, beneficiary, creditor, IRS) shows up to contest unauthorized actions, people can get away with things that aren't authorized.
A will is supposed to be filed with the County Clerk within 30 days of someone dying. If it is not so filed, whoever had custody of it may be liable to someone who is damaged by not filing it.