Mathilde is one of the older Goetz dolls that share the American Girl body.
There is little information available about these dolls.
They seem to have been produced in the late 1980s and early 1990s as limited edition collector´s dolls (rather than play dolls). While “Mathilde” seems to be the name of the sculpt, there is apparently no character back story.
They come up on ebay occasionally and from the auction descriptions, I have learned that they were produced with glass eyes and human hair wigs and were really expensive (one seller said the doll originally cost around 350 DM, which is 175 Euros today, and, in 1991, would have come to more than 200$). Some were limited to 100, others to 150 dolls.
Here are some more examples, all pictures from completed ebay auctions:
This Mathilde-sculpt doll was named “Monika”, another limited edition according to the auction description.
Cosplaying as Lilo.
And with a wig that suits her better.
Mathilde´s sculpt lets her pass nicely as an Asian girl.