Assume Silver = BA Silver?

If so, for lounge entitlement doesn't matter whether you are flying domestically or internationally.

It is only AA who deny their own frequent flyer scheme members free lounge access when flying domestically, the oneworld rules make no such distinction, and AA has to give it to you.

I don't know the airports in question, if there is a oneworld airline lounge (e.g. an AA lounge, a BA one, or etc) in the same terminal as your flight departs, then you will have access to that using your BA Silver card (OW Sapphire).

If AA have a third party contract lougne, that they use for their business class customers, etc, then they should also give you access to that, due to you Sapphire card.
[The fact you are in economy is irrelevant.]

If however, they do NOT have a contract lounge, or their own branded lounge, at an airport (i.e. they don't give business class passengers a lounge) they are under NO obligation to prove you with access to a paid lounge, even if one is available.
[Of course, if a OneWorld lounge was accessible in your terminal, you would have access to that, even if, for some reasons, AA did not give their own business class passengers access to that lounge, etc.]