I've seen these envelopes(there are cards that match up with them)in the greeting card section upstairs at the Long Beach Barnes and Noble. I think I sent one of my nieces a similar design. I think they're wonderfully drawn.
Ah yes, the "Rabbits of the Rainbow" series by Pamela Silin-Palmer. I have a large number of them collected for use in various occasions. Perfect for SCA & Faire types, Christians, and of course bunny lovers.
You can see more of her work at www.pamelasilinpalmer.com
Your mom must have good taste!
Ahhh..okay...now I see the envelope...
You can see more of her work at www.pamelasilinpalmer.com