Personally I think it would be a wonderful idea to name your daughter
Gladys after her great-grandmother.
However,
Gladys is probably not quite ready for a comeback with the general population, precisely because it's a name common in your own grandmothers' generation. Usually it is the names of the great-grandmothers of the young parental generation that are likely to "come back". When most people remember several former elderly bearers of a name, it tends to still sound "old and ugly" to them. It's only when most young parents never knew the previous generation when the name was popular, because most of them had died by the time they were 10 years old or so, that a name can "come back" strongly. So you would be ahead of your time to use it.