Charles Parker Company bent glass panel lamp

My grandmother passed recently and in the upstairs bedroom left a note tucked under this lamp.  The note says the lamp is a Charles Parker Co. lamp, which we confirmed by looking under the base where the company label is seen on the bottom. 

The lamp 'shade' is itself is quite wide... about 16" or more I would guess.  (I haven't measured it yet).  The base is extremely heavy.  The lamp itself is in very, very good shape and does work.  The metal overlay on this slag glass is also quite decorative and free of rust. 

The family is wondering what the lamp may be worth.