I have had the first part happen 5 or 6 times years ago before I switched to filing online with the SSA,
but it was always resolved by responding to the first letter and mailing in the W 3/W2s.
Yeah, the Tax Advocate is swamped.
At this point I think the best option would be for her to contact her Congressperson who usually has a designated staff person to handle tax issues.
If you do that, you will need to have everything clearly documented and explained. They aren't going do research for you!