Do both of these boards have the center fin slot?
I know the Starsurfer has one, but not sure about the PK Go.
If the PK GO has the center fin, I would go with that as it's wider.
I did some testing on the 117 liter Starsurfer that I will share with you
if you get that board. You really need to get your daughtter a 2.5 m2 rig
as soon as possible.
The mast slot to center fin distance makes it nearly impossible to stay
upwind on this board with sails < 2.5 m2..
The PK GO may very well have the same issue.
Tiny sails have the COE (center of effort) very close to the mast, and the CLR (Center of Lateral Resistance)
is too far back to get upwind drive without raking the rig so much that it makes almost no drive.
A mast track extender, or a new single mast position right over the front of the center fin solves this issue.