In my opinion, if you and/or your girls liked the movie "Legally Blonde" they will love the musical . . . it was very true to form. My two younger girls (12 and almost 10) loved the two movies and LOVED the musical . . . my older (almost 15) isn't a fan and didn't care for the musical. (She's a huge "Spring Awakening" fan and I will be taking her back to see that for the third time today at 2-- we have the seats that are right on the stage.) As for me, I can't say that "Legally Blonde" was my favorite B'way musical, but it was a pleasant enough way to spend 2 1/2 hours.
As for "Little Mermaid," I'm sure I will take my girls to see that. I have some sad feelings about it, though, since it is replacing "Beauty and the Beast" which closes in July. One of my best friends has been a violinist in the orchestra there for many years, has taken my two oldest with her into the pit during shows, we've been to Central Park to cheer her on when the Broadway softball league plays in the summer, etc. "Mermaid" only has two violins scored while "Beauty" has six, so she and three others are losing their jobs. Now she has to start looking for another show with an opening, and hope that the show makes it!
As for the foreign exchange student, I agree that "Wicked" is a must. When you get to know her a little better you will be able to see what other shows she might be most interested in -- "Legally Blonde" "Hairspray" "The Lion King" and "Mamma Mia" come to mind . . .