I've run into this issue for many years with Starboard's mast slot placement and
tiny sails like your daughters 2.7 m2.
Put the mast foot absolutely as far back as it will go.
The tiny sails carry their power really far forward, right up by the mast, so to get any kind of upwind performance you need to move the mast foot as far back as possible.
Also, she needs to tip or "bank" the board by moving her weight slightly off center toward the upwind side.
This will "engage" the upwind rail and rockerline and help her to go upwind.
Hope this helps,