Lots of things made it through WWII. Bringing that up (it survived the Arab oil embargo, Iran-Contra, WWI, the Spanish-American Influenza, 9/11...) is just rhetoric to drive home that it was more than a century old.
'Erica' is selling a "French violin".
WW II had a couple of unfortunate local consequences for France.
Most of the list of things you mentioned might be perfectly irrational to name in a letter. WW I or II are good examples for 'Wow, it survived' remarks on local pieces of craftsmanship or art.
WWII treated France pretty well on the brute destruction scale. France didn't even lose most of its sovereignty after the invasion, with the Vichy regime resisting German demands when it wished to.
They didn't go through anything like what Japan, Germany, or Russia did, with the cities razed by fighting (Stalingrad), fire-bombing (Tokyo or Dresden), or atomic bombs (Hiroshima & Nagasaki). If a French violin had survived the siege of Stalingrad - now that would be impressive. But just being in France? That's about as impressive as a random Englishman surviving the Battle of Britain.
Saying that a violin has survived the oil embargo would not make any sense. Saying that this brittle musical instrument has survived a brutal war does make sense. Especially in contrast with its (allegedly) not having survived a legal dispute.