RE: What planes faster...?
I will also add that she will need to get the rear foot into the strap to make the F-Type "work" well.
But it does have an inner step of strap holes, which I used for a while when I first got the board and was trying to figure it out and get used to it.
BTW I just started shortboarding last year, and went from a Start to the F-Type (similar to her GO at 90 cm wide). Remembering that transition myself, going to a GO 139 would probably being the easiest transition for her, but going to the F-Type or Carve would push her to progress more if you think she is capable of it. (It did push me to progress, but was tougher at first.)
If you want her to be able to just leisurely plane around in the front strap only, and work her way up to getting in the back strap, then maybe the GO or Carve is a better choice.