On Isilme, Adalwulf's dragon had an egg which she gave to Gunslinger, I believe, so I don't see why it couldn't be the case here? To my knowledge not all eggs are abandoned - there have been some events I'm sure where the egg's parent gives it to a character out of choice. Cynder would simply be giving the egg to her bonded's daughter as a gift then leaving Helovia alongside Tyra. It would just make it more interesting than 'oh look a random egg' and as I say not all eggs have been abandoned in the past :/
[ we are made of greed ]
[ the regime ]