Just give her the powers and leave

Deumos hummed while tapping her chin. Glynda Goodwitch was a professor, and likely smart gal. She will probably figure it out by herself.

She made up her mind, and simply tapped Glynda's temple lightly, transferring her power to the blonde woman, or at least a 'copy' of it. It took a little while, such was expected with the sheer amount of power the Demon Queen possessed and such a delicate process shouldn't be rushed.

Finally done and satisfied with herself, Deumos left Glynda alone.

The professor would be in for quite the surprise once she finds out...