I think there are multiple meanings in there.
The one I would use is that the egg symbolises her dislike of her father, her resentment of him.
'hated my self, hated the egg
growing in secret deep inside my body,
the secret about to be spilled
to the world, and maybe I did.'
She kept this inside, secret, hidden, locked away in a shell, until this egg hatched with her own mistreatment of her own child.
'Or maybe it's the way the egg
repeats itself again and again, a perfect
oval every time, the way I found myself
furious, standing by my own child's bed
holding a belt, and hit, and saw her face
dissolve in yolk. But that doesn't say
enough about why we hoard
our hurts like golden eggs and foolishly
wait for them to hatch'
It would have been better to break the egg, speak to her father, and get her resentments out in the open, rather than let it grow inside and come out to harm her child.
'never once picked up
those perfect ovals and sent them singing
back and forth across the room, the spell
broken like shells, until we were
covered with them, our faces golden
and laughing, both of us beautiful and flawed.
I hope this helps!