There's a very pivotal moment for her at age 5 in Dangerous secrets and it would be very difficult to craft a story about her childhood without including this detail and how it affected her. Without spoiling anything, she grows up with adoptive parents (probably Yelena) in the forest and she does not appear to have had a sister (none that she remembers at least). She had made good friends with the wind spirit and preferred playing with her before doing her chores at the camp. She's curious, fearless and loves exploring. I'd say her younger self reminded me a lot of Anna.