Lying is definitely NOT the way to go. Even though the whole "Oh that, I've had that for a while" is pretty funny. It would just cause resentment and anger toward Mike's snake hobby.

I think if you sat down with her (make her dinner or go to a nice restaurant) and said you needed her help to make an "executive decision" about your breeding plans she would be exited you want to include her and want her help. Try to show her WHY its a really bad idea to sell your breeder girls BUT how much better your collection and future breeding would be if you held back the VERY best of what you produced this year. But don't say "can I keep..." instead say something like "I would need to hold back..." Get her involved with the "business" and collection end of the hobby if she's not in to handling them and caring for them. Plus it is always great to get involved with her hobbies too even if its just talking about them not actually participating. Also, the idea of using the profit from sales to do something together is a huge incentive for you to increase your collection.

Good Luck