Just because a four year old is not interested in playing piano I wuld not give up on her just yet.

Maybe buy her a little small keysize multivoiced electronic keyboard to play with rather than on?

It has taken me 50 years to find keyboard instruments of any kind at all interesting, even though we had an upright piano at home and my mother and sister played, my mother's mother had a really ancient looking piano too, I think there must be a piano playing gene.

Anne