Can Sona's ability be countered even if her effect resolves at the end of the turn?

Ruling: Sona's ability is a triggered effect that you can react to during the end phase, but there is no clear method to counter it in Riftbound.

Nuances:

• The ability being a triggered effect means it uses the stack and can be responded to
• Despite being reactable, no specific counter mechanism was identified in the discussion