There are a few slight differences with gen, methinks. Notably, the 'CHANEL' font on the dial should be a bit bolder than the 'J12'. Perhaps a slight difference in size/shape/color of the hour indicies? I've never really paid that much attention.
Bezel shape is fairly similar, except I think the bezel teeth are a little less pronounced on the gen.
A few other small details, like caseback engraving, clasp engraving and the sort are usual standard rep fare; not deep enough.
Othrwise, it's a very nice piece. I've never had a gen J12 in hand to directly compare, let alone to take apart, but I think the case construction is the same:
And the white ceramic links are quite nice. They have an almost opaque translucent consistency when held to the light.
Mrs. Ubi is very pleased with hers.
While we're on the subject of Ladies' J12's... Someone is pulling a no-no and listing a rep as gen on eBay...
Item 220726991278; BIN at $3150!
How do I know it's a rep? Compare their caseback with Mrs. Ubi's:
Hopefully they just don't know any better...