How should you act if you thing your dc is on the verge of an eating disorder?

[Alwaysaboutfood]

Panicking as my dd has started over last few days being funny about food. For example, last night she announced she only wanted to eat peas and sweet corn. This morning she said she only wanted an apple to eat. I've seen her Google history and she's been looking for supersize/super skinny ( as in the tv show).
My dsis was anorexic from 16, I became bulimic from 19- 22, but it flares up from time to time, but is largely cured. I am very very paranoid aboutmy dd aged 12 going the same way. I really don't know how to deal with it as I'm scared of doing the wrong thing now.