Throwing away children in silence was unusual.
In addition, it was a child that had talent for becoming a magician—seems like there was a good reason for it.
This might be an unpleasant way of putting it, but, if she became a magician she could earn them lots of money.
Even if they're poor, there was no reason to let go of the golden egg.
If they wanted money quickly at all cost, they should have sent her out to some childless rich and powerful people as an adopted daughter.