You are walking into a minefield here! Everyone has their own prejudices em - preferences.
Have a look at the Chiff and Fipple website. That has a pretty comprehensive review of different makes of whistle.
I will air some of mine. I like the generations for playability, but they are notorious for poor quality control and they can be very out of tune. Clarke Sweetone are generally in better tune, but I personally am not that keen on them - I stress, this is purely a matter of personal preference. I have a Susato which I like. I think they have many of the virtues of the Generation with added advantage of being in tune. I don't play it all that often as I prefer recorder, but I find their C Whistle very useful as I can play it with Northumbrian pipes as if it were a D.
I think for your daughter, it is vital to start her off with something that is in tune.