Sandra was seen in one W.I.T.C.H. episode - season 1 episode 7 - Divide and Conquer. She came to Sheffield Institute, pretending to be from Switzerland, only so that she wouldn't be a lonely girl and so that she could be popular. Sandra made a big entrance, walking through the doors of the cafeteria. Instantly, nearly all the boys there, fell in love with her.
Later on in the episode, when they are at the ski trip, she and Will have an argument. They both like Matt so, the set up a ski competition, first one to the finish line gets to sit with Matt on the bus on the way back. In the end, even though it's terrible, Will wins the race and Sondra ends up with an injured leg. Sondra starts speaking grumpily and has a non-Switzerland accent. Everybody finds out that she isn't Swiss. She then decides that she should transfer to a different school. All of the boys - except Matt - are still in love with her though.