Good for you for doing the right thing! This community makes me proud.
Judging by your description, this sounds like a transitional kit. 3-ply shells point to pre-1957, but silver interiors point to post-1957 or so. As I understand it, they switched to silver interiors at the same time they switched to 6-ply shells, but you do see plenty of transitional 3-ply kits with silver interiors.
The Gladstone FT mounts are likely 1950s. They started with the interior paper tags around 1962 or '63, so my guess is you're looking at a late 50s kit. (I've got a midnight blue pearl kit with the same transitional specs: 3-ply, silver interiors, no tags, Gladstone mounts. It took me forever to figure out its age.)
The thing that confuses me, though, is the rims. The triple-flanged rims on the rack tom are definitely not original. '50s Gretsch kits had double-flanged stick choppers; I didn't think they started using die-cast hoops until the '60s. I could be wrong.
It's worth checking with the owner to see if she has the cymbals and other goodies that came with the kit. On a Gretsch kit from that era, the cymbals might well be Istanbul Ks.