When Stellacorn with Ride the Wind moves to my battlefield ready, but gets stunned by Thownk and recalled back to the base, is she ready?

Yes, the unit will be Ready when it returns to the base.

According to Rule 453.1 and the Recall clarifications in the patch notes, recalls do not affect the state of the permanent being recalled. Unless the source of the recall specifically states otherwise, any damage, exhausted status, or ready status remains exactly as it was on the battlefield.

Here is the breakdown of your scenario:

1. Ride the Wind: You play this spell to move your unit and ready it. The unit arrives at the battlefield in a Ready state.
2. Thwonk!: Your opponent plays this spell to Stun your unit. The unit is now both Ready and Stunned.
3. Recall: When the unit is recalled to the base (e.g., due to combat resolution or another effect), it retains its current state. Because it was Ready when it was recalled, it remains Ready at the base.

Note: While the unit is Ready, it is still Stunned. It will remain Stunned until the beginning of the next Ending Step (Rule 423.1.a.2). Being Ready allows it to be available for actions, but being Stunned prevents it from contributing its might to combat damage if it were to fight again before the Stunned status wears off.