When did the tax preparer go "silent"? after she received the 2021 stuff? the 2022 stuff? the 2023 stuff or did the client send all years at once? 

Either way, this will fall back on your client. If client was already late when they gave the stuff to the preparer it is their fault. If the client kept sending stuff to preparer year after year without acknowledgement, then that is also on them.

Do you even know if the preparer is alive? Maybe they died or had a major health issue - I'm not sure they "stole" her paperwork. Of course, if they were not going to do the returns they should have contacted your client and sent all the paperwork back. BUT - really IRS will just say she should have requested new or duplicate copies from the original issuers and filed on time.