My 7 year old DD loves lego friends. She also plays with the regular city sets her brother gets and she wants some of those sets too. She recently used her birthday money to buy Olivia's House, and she and the neighbor boy (6) spent all afternoon putting it together. He's very jealous and wants the friends house too. The friends sets have so many cool pieces that aren't available in the city sets. I can see some sets are more "girly" than others (like the beauty salon), but many of the others (vet, cafe, treehouse) appeal to boys and girls. My kids are much more likely to fight over friends pieces than city pieces. I agree that the friends sets appeal to the type of play the girls like (role playing). I'm sure DD will want the girl minifigs.
DD (3/06)
DS1 (7/09)
DS2 (8/13)