Noguchi table disaster  

Dimensions are available easily
If you go to the HM site you can get the glass dimensions directly from the table's cut sheet. Any reputable glazier should be able to duplicate them.

The Vintage Noguchi Glass tops were unsigned...
Therefore,why spend the money on a HM one.I agree-glass is glass,and the possibility of anybody detecting a non HM top is so slim.Besides,the cost would be MUCH less from a reputable glass co.The template can be obtained online,I believe.

the name...
The signature inscribed on the glass edge...is it really etched? because when I worked at DWR the one in our showroom had the name rubbing off...Are they silkscreened instead?

the one I own is 2 years ...
the one I own is 2 years old and it is etched in the glass

Lots of info
But - I would side with the 'buy from Herman Miller' people here. Your friend HAD an entirely original table. She clearly had kept it in her family, and despite the fact that accidents happen - she should still have an original table.
Replacing the glass through a third party just seems like a mine-field of potential mistakes. The Herman Miller glass will be the correct shape, thickness, and close to the original (altho the edges are darker)
A little bit of black lacquer worked into the scratches on the base should hide most of them, then hit the whole base with a coat of paste-wax to even out the surface finish.

Just a few comments...
SDR is right in explaining that the green is the result of a slight coloration throughout the glass. I suspect that there are many versions of green because it is soemthing that is very difficult to control. Usually nobody notices, but when it is thick glass it becomes more obvious. Only crystal is completey white...but so much softer.
I understand the concern about braking and I definitely agree with having security glass in doors etc. but...tempering glass is a treatment that affects the surface of the glass. It is very sensitive to scratches and this being the surface of a teble...I think I would rely on the thickess to keep it safe.
One thing nobody can avoid is that this became a table with a history. A new glass with etching from H.M., a vintage one prior to the time H.M. did the etched signature, à local made one, they will all tell the same story....and all the kings horses and all the kings man could not put Humpty Dumpty together again

thank you
for all of your help. I have emailed my friend with a link to this thread so she can see all of her options and make her own decision.

Oops, I was wrong..
...it's only doors that are required by law to have tempered glass (or acrylic). Tabletops can be regular plate glass, though I'd never have that in my house after my kid's accident.