What is her skill level now?
What size sails is she using?
48 cm is about right for the width of that board for 6.5 m2 and up.
You migt want to find a 46 cm or 42 cm.
Do you have weeds on your lake?
Did the GO 144 come with the 41 cm Shallow water fin?
For winds > 18 knots, the Go 144 will become quite a handful.
Do you have any smaller boards she could use for the higher winds?