There was much talk about that and after looking we determined that the whelps had to hatch withing 10 seconds of her lifting off (not sure if it's 10 sec before, after or both) and she was at still above 95% when she knocked me over the wall.
But we did decide that next we'd go for achievement and just have tanks run into caves while she's headed back for liftoff. They were pretty easy to pick up when you're in the cave with 'em.

