Can a wild shaped druid reply to Message?

The wizard casts Message and targets my druid that’s currently a wolf.

Wild Shape mentions:

You can’t cast spells, and your ability to speak or take any action that requires hands is limited to the capabilities of your beast form. Transforming doesn’t break your concentration on a spell you’ve already cast, however, or prevent you from taking actions that are part of a spell, such as call lightning, that you’ve already cast.

Message states:

You point your finger toward a creature within range and whisper a message. The target (and only the target) hears the message and can reply in a whisper that only you can hear.

The druid can clearly understand the message. So far my DM has ruled that I can’t reply because I can’t ‘whisper back’ as a beast. We are curious to whether this ruling is correct.

In other words: by RAW, how important is the ability to whisper while replying to a message?