It looks like she may be here to stay. She was on today's show, as well as in the opening (Partial funding of Sesame Street is provided by...)
It looks like a lot of old characters get ressurected over the years...
In 1993, they brought back Frazzle, who was previously thought to be too scarey for kids (he was written to be softer, and more child like)
There was a point in the 90's where Sherlock Hemlock seemed to be in a few sketches.
Last year, the Amazing Mumford appeared in quite a few skits.
Not to mention the Two Headed Monster, who came back back last season, and appears in Journey to Ernie....
So Gladys may be here to stay... cool!