When using "Flower Shop Lady", do I have to put all 3 Pokemon and all 3 Basic Energy cards into my deck, or can I choose to return only 1 or 2 (or none) of each?
You must return all three of each if you are able to (or as many as you can if you have less than three). The card does not say "up to 3".
Source: Undaunted FAQ (2010-09-09), PUI Rules Team (2010-09-09)

Relevant cards

Note: All applicable cards may not be listed below.
HGSS3_74