Theory on what happened to Anna?

I think The Snow Queen has her and is gonna threaten to freeze Anna's heart or has already done so but making the freezing process slower and wants Elsa to hand over her powers to her so the Snow Queen can be more powerful and if she doesn't, she'll let anna become completely frozen so the next time we see Anna is in the SnoW Queen's captivity slowing freezing to death. (Of course i have faith Elsa and the others will be able to save her)