The Reagan Inauguration was on January 20, 1981:
January 20, 1981 -- Ronald Reagan
Outdoor band concert was held on the West Front lawn on the day before the inaugural.
First inaugural held on the West Terrace of the Capitol.
First time that room EF-100 was used as a holding room.
First closed-captioning of television broadcast for the hearing impaired. (Washington Post, 12/22/1981)
First post-inaugural luncheon held in Statuary Hall.
Post-inaugural luncheon was partially televised.
Nine inaugural balls were held.
First time that an inaugural ball was held in a legislative building (Rayburn House Office Building).
Balls were transmitted by satellite to 32 ballroom sites across the country. (Washington Star, 12/19/1981)
http://memory.loc.gov/ammem/pihtml/pinotable.html
Maybe Judith was at the outdoor concert on the West Front lawn that was held the day before the inauguration and this would be the news clip where Judy's sister saw her.
On the Still Looking for Judy fb page, a family member recounts how they saw Judy being shown on the ABC nightly news during the NYC sanitation strike. The NYC sanitation strike during this particular period of time started December 1, 1981 and this would be more than a year after the last reported sighting of Judy in Baltimore.
That is a whole year of no contact which is odd since Judy hitched from NYC to Minnesota (IIRC) to her g'mas party so she was a family oriented person for special occasions. Judy was also in Alabama in 1980 to visit a sibling prior to the birth their child.
From November 30, 1980 in Baltimore to the recounted sighting of Judy on the ABC news which would have been in December 1981 = a huge gap with no family contact. Was she perhaps incarerated or hospitalized during that period.
This is really as far as this can go with information at hand. Judy please let it be that you are found and may your sister have the continued strength to carry forward to find you.
eleph