Sounds like this is a lesson for you.
Maybe your mom should read the posts made about your concern and response.
I'm married not living at home with my parents... but SOMETIMES... it's easier to ask forgiveness then permission.
Is this your hobby or Mom's? What is her reasoning of putting him in even without quarantine.. or look but don't touch even? Why did YOU buy the rooster?
No judgement... I'm just curious about peoples thought process that leads them to their choices.
Leghorn are pretty good at evading affections they don't want, and one reason why a rooster would treat them differently. If they aren't willing to mate he don;t want them taking resources from the hens who are. So you don't have any actual bantam ladies?
As stated by others your resident males are the real concern. Hope it works out quickly!