Recently my wife purchased an older but very nice porcelain angel doll.
It was complete other than missing a musical instrument (mandolin) that it originally came with.
Searches did not locate one in the proper size or one that was affordable for sale.
Nor did I find a suitable model on 3D printing websites.
So I designed this one for her.
It is dimensionally and proportionally as close to the original as I could manage.

There are two versions attached here, a smaller one that is approximately 2.6" (65mm) in length, and a larger one that is approximately 5.25" (133mm) in length.
The larger one was perfect for the size of her doll.
Either of them can easily be scaled in your slicer.

The one shown was printed in black ABS, but any filament material or color will work.
After smoothing and filling it was painted using dark brown, light brown and gold acrylic paints.
The strings are made from carpet thread and they were routed between the holes on the back of the instrument as shown.
There is only a single piece of thread that is secured by knots at the lower tuning pegs as shown in the photos.
Dabs of the darker brown paint were applied to the back side to seal the strings into the holes.
The colors and general paint scheme were copied from photos of the missing instrument taken from original advertisements for the doll.

Note that you will need to drill holes for the strings in the smaller model, but that the larger model already has holes present.
They will very likely need to be reamed out with a 1.2 to 1.6mm drill after printing and painting, but at least they will serve as pilot holes.

This was a fun project and it turned out nicely.

Thanks for looking. Enjoy.