My opinion is based on the bar conversion.
Get what is very comfortable for her this season. I assume she rides quit a bit now. Then when she shows interest in drop bars buy her a drop bar bike.
If she might be ready to try a drop bar bike this year you save a step. If she is hesitant, then make her happy.

Enjoy riding together above all. Remember to stop and smell the roses.

-Snuts-

Edit: I see she is relatively new, looks like a season on the flat bars. Trekking bars are an easy upgrade later, for touring.