Linnea is the fourth person from the left in pink, in the second row behind her friend Alex (and Gemma, if you can spot her!).
First the little ones dance to "Super Trouper" and then they run off, but you won't see the whole 'Mamma Mia' number unfortunately because Lucas turned the video camera off when Linnea wasn't on stage, ha ha!
They come running on again, and they all finish off together, all three groups, with "Dancing Queen". Linnea is to the right, but hard to see, she can maybe be spotted by that big bun in her hair?