Low volume bookshelf spkrs that go from 20 to 20k?

Hi folks, My daughter (9 years) is a discerning listener and a trained singer. I want to reward her with a nice stereo system. We listen to music at low volumes. I plan on buying speakers on my next trip to the US (daughter can not audition speakers). I do not want to compromise on quality but have a budget of about $ 1,500 for the speakers. The size of the room is about 14 feet square.

Speaker requirements:
Freq response: Should cover the audible range (20 to 20khz). I think this will keep my daughter happy.
Model: Bookshelf preferred (small room)

My questions:
Will I need a sub to complement the bookshelf speakers?
Are there bookshelf speakers that cover 20 to 20khz?
What models would you suggest for bookshelf and if required a sub. A 220 volt power supply for the sub will be ideal but not a must.

Appreciate your suggestions.

Vish