Emma and Elsa were ‘cousins’ (!?): Emma-DQ-Elsa’s mother-Elsa & Anna
Fostering someone doesn’t make that person related to you by blood. The only way Emma would be related to Elsa and Anna is if she’d been legally adopted by the Snow Queen/Sarah Fisher (assuming, of course, that the Snow Queen was telling Elsa the truth about being her and Anna’s Aunt).
Also, given the context of the scene in which we found out what Emma’s connection to the Snow Queen actually is, it seems far more likely that she (the Snow Queen) was the matron of a group home, which would only make her a ‘foster mother’ for Emma in the most broad sense.
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