I would say it depends on the weather. If it's not too lumpy on the outside, that is the way to go. Many nice reefs
to stop and snorkel, most of which have free moorings you can pick up. Sombrero. Alligator. Coffins Patch. I would sail outside then duck in at night. Check Active Captain
for a nice anchorage near your locale.
If it starts getting lumpy, you can jump inside at Snake Creek or the Channel 5 Bridge in Lower Matecumbe and do the ICW
. It's a lot more dull on the inside and basically no good snorkeling.
Boot Key Harbor in Marathon is a must. You need to stop and get a deep fried Key Lime Pie at Burdetts.
Have a great trip. BTW, the Keys Beaches are notsohotso, so tell your teen she may want to tan on the foredeck.