The sizes of recorder I use most are in G (alto and sopranino). The reason is that I play a lot of Scottish tunes, which often use the pipe scale (nine notes G A B C# d e f# g a). If you play those on a G recorder your fingers will often be in the same places as they would be on a pipe chanter, so they feel more natural. Good G recorders are not cheap, but there are altos and sopraninos from Susato that work okay so long as you don't want to use the very highest notes much - they're good and loud in the range where it counts for Scottish tunes.

For a ten-year-old, an alto might be manageable, depends on how big Ava's hands are. It's worth getting used to switching sizes as early as possible, as recorder players do a lot of it.