A woman thought to herself that she will have to provide herself with a pair of plain-lensed glasses.
Does it mean just regular glasses with transparent lenses?
I think so, yes. I assume it means lenses with no colour or tint, not bi-focals or vari-focals etc. It could also mean that the lenses don't even have an eyesight improving quality. Perhaps they are just glass lenses which don't have a "strength" so they are just used for appearance of as a disguise.