why snow fairy cant kreuz the border, while in the 1st movie they came to pixie dust tree?

i watched Tinkerbell: Secret of The Wing last month.
And today i watch Glöckchen 1st movie.
i am little confused. in the Secret of The Wing, snow fairy cant kreuz the Border. But why in 1st movie Cera (snow fairy, i know her name in Glöckchen Lost Treasure NDS) and minister of winter came to the pixie dust baum when Glöckchen looked for her talent?