Antique Victorian Art Pastel Painting Portrait Woman Signed A.T.G. ?? 5/64

We found this portrait in a thrift shop. My fiance has an eye for art and quickly took it home. It is very well maintained, looks to be professionally framed, nice gold wooden frame and the glass is very thick.

I appears to be a pastel of some sort, of a 17th to 19th century woman we think,

The signature is a little difficult to understand, looking at it we see initials of T.G but in the pictures it appears it could have some kind of third letter like A.T.G combined together. Also, it is numbered we think as well with 5/64.

Any insight would be wonderful as we have both tried to research the artist and the drawing and have come up empty.

Thank you 

Christina and John