To keep it secret or reveal it, all upto you.

But I do learn something from her, that... if someone ask a favor to keep a secret, I should never say yes! unless I know whats the deal?

Anyway, I just said "IF" I am in your shoes, I will be kind enough to teach and show her how to do her task. But the next time, she should know and learned to do on her own. Wouldn't do any harm for me to share my knowledge with her during my spare time but certainly NOT when I got load of works on my desk. After all, its for the benefits of both... hers and my company. I shouldn't forget that I started from zero work experience like all of you.

But things would be so easy if she has keen interest to learn. And that's the main question...is she interested in learning? If you feel that all she wanted is for you taking over her task....is a big NO!

It should be,.... instead of her asking you to do the job for her "secretly", she should be asking you politely "how" to have it done properly.