Saint Theresa Large (Catalogued) Bronze, But Silver?

Exact diameter please.

If lamoneta is of no help you have to ask in italian forums. And good luck because you will need that.

It is very common for medals to be struck in different metals. For restrikes to be made many years after the original. All it takes is a collector wanting one and paying who has the dies. You can be sure it did not happen only if the dies are locked away, as stored in some state archive. Or are known to have been destroyed.

I once saw for sale one 150 years old medal that was recorded as unique in the reference book for those medals. But the national museum had one. And a historic collection catalog listed another one. So there were three at least.
I bought it cheap and set to research. Found a newspaper of the date of the event: a gold medal had been struck for the person receiving the homage. The reference book mentioned a single medal struck, and listed AE as the metal. Wrong information. A couple in silver were also struck for the monarch and mayor of the time. And it was ordered from a private shop. A dozen years later a bronze one is reported in the inventory of that private collection. The shop owner must have seen a market and struck on demand for collectors.

Some very few medal issues, official ones by state mints, specify in law that the dies are destroyed at the end of the striking. Those issues have trustworthy numbers. Most official issues by states have the dies kept in store and used once in a while for restrikes. Those are documented and should be trustworthy.Where the state was not corrupt or fell into anarchy. Or if the issuing was done at the Paris mint. That one cannot be trusted, they struck on demand for a long time from the dies they held.

With commercial issues of medals anything can have happened. Dies are traded and reused. Can happen centuries later.

Yours looks like silver but can be some white metal or silver coated. Density test and surface tests required to be certain. Have you had it testes? Do not forget contributing the info to lamoneta after.