OK, I have the picture....
I'd suggest a couple of vario rake weed fins.
The vario rake "shallow water" weed fins from True Ames (Shallow Water Weed),
and Tangent Dynamics (Tangent Reaper) would do the job, and they do not stick out
dangerously behind the board like the 50 deg. rake angle weed fins from other sources.
I also like the Wolfgang Lessacher Duo Weed fins, but you would need to get them directly from Wolfgang in Germany. (He does internet sales, so it's possible).
I'd look for the a couple of weed fins in he 32 cm-38 cm range.
One fin around 34-36 cm would really be all she needs.
In Bonaire, she was probably sailing on a larger fin cut down to 32 cm, so that size should work.
A good quality weed fin (that does not stick out the back of the board dangerously) will get her going just as well (and just as fast) as a vertical fin, at her skill level.
If she is going to stay under 6.5 m2 these fin sizes will work nicely.
Hope this helps,
P.S. If your < 100 liter boards are fairly modern and wide, and your wife is fairly light in weight, she could fool you as to how easily she could adapt to the smaller boards.
What was she sailing in Bonaire (brand/liters)?