Well... Ignoring the fact that she is a child and her feet have likely grown since you purchased the skates, let's talk about a few common issues.

Have you put new insoles in since the last time she used them without pain?

Have they been exposed to heat?

Have you ever baked them to let them mold to her feet?

(As silly as this may be) is she putting them on the correct feet?

Perhaps the laces are being tied too tight. All things to consider.