Okay, so when I was maybe 7 or 8 (so in 2005 or 2006) there was this show/movie I came across on Scifi.
I don't remember a WHOLE lot about it clearly, but I remember there were two little girls, sisters, and they were running around together gleefully through the woods. They ran into a witch, and the witch couldn't harm them if they were together, but the younger sister got scared and ran away and the older sister got snatched by the witch when she did. Thus the older sister became an evil witch herself and the entire rest of what I saw was the adventure that ensued, the younger sister I think not even remembering that it's her fault her sister is evil.