For the record I started sailing at age 10. My friends had each snarks... one had the snark sandpiper (4 foot wide tub with a dagger, and 2 bench seats):
The other had a snark wildflower:
Later that year I got my brother's sunfish for myself. I was WAY faster... BUT... my tiny 100lbs wasn't enough to stand it back up! The mini-fish is probably easier, but the hull is still too heavy to deal with for a kid that age.
The optimists are OK... and with a dolly, can be more manageable for a kid (it's the size more than the weight).
Honestly, the easiest boat to deal with was the Sea Snark that was mine the following year. It was 100% foam (super thick). It was light (30lbs hull, at 11 feet long!)... and rigging was stupid simple. The boat wasn't a sunfish fast, but it sailed, and was tough as nails!
Mine was so tough, that 31 years later my brother still sails it (just for kicks). He had to sew a new sail for it, but it works great!
My point is, I'd be looking for a super snark (ABS plastic over styro), or Sea Snark (100% foam). They were light, can be purchased all day long for $200, and are simple to car top.
Once she's really into it. Get her a real sailing boat, like the minifish, or a laser pico, or open bic... by the time she's 13 you'll be looking for a full out laser.
PS: My daughter is going on 10 now (next month). She's just starting to like sailing (she road out a light rainstorm with me last year that drove us in 25+ knots, a wild ride for sure and she loved it)... but has no desire to try it herself. How do you get her to want to do this herself?