The Artistic Mother Art Group that they were hesitant to move forward with the Butterfly Reminder project from Week 5 of The Artistic Mother by Shona Cole because they were concerned that the balsa wood would crack when they drilled their holes, and that is a possibility. To avoid that from happening, what you can do is make a starter hole with a smaller drill bit, then proceed with the 1/8" (ISO 3.2mm) drill bit that the book recommends. Just take it easy going in a little at a time. I would suggest practicing this method with a scrap piece of balsa wood before attempting to make the holes on your butterfly. I hope this helps. I didn't have any problems doing it this way; so you should be fine.
Please let me know if there are any other concerns or questions with any of the other projects that I might possibly be able to help you with.