I've been to Menorca a few times, but only once since having kids, so I'm afraid my knowledge of family friendly places isn't great.
Binibeca is lovely but very quiet (good for younger kids, prob a bit dull for older ones).
Fornells is the big watersports area so if they want to go sailing/windsurfing/water-skiing etc, that's the place to go. I'd assume it's got a decent nightlife too as it gets a lot of bright young things on watersports holidays.
Unless she's after England del Sol, avoid Cala'n Porter like the plague - it's certainly lively but only if you like chips and lager with everything. Last time I went (caveat: this was a long time ago) it was impossible to find a bar where the staff spoke Spanish. We didn't stay long...
Mahon is probably the liveliest bit I've been to - there's a whole stretch of restaurants along the harbour side plus nightclubs if they're into that sort of thing (not sure whether they're looking for ents with the kids or hoping for a night off!) Also lots of tourist traps shops.
Es Castell is a bit further down the coast but also has a handful of restaurants on the seafront - it's nothing like as busy as Mahon but considerably prettier. Depends what they're after.
You say you've been to Sa Caleta - did you get a chance to go into Ciudadella? I've only been during the day (having stayed at the other end of the island) but that's also got lots of restaurants and, being the old capital, has a certain amount of cultural stuff to see/do too. I really liked it. Some decent beaches nearby too.
Wherever they go, I'd recommend hiring a car if they can afford it. Then they can try out different places and won't be tied to the resort restaurants/shops (which can be overpriced, especially the shops). Also, because it's such a small island, you can see a huge amount of it in a week - and try out a different beach every day!
Hope that helps a bit.
Alice