Do you have VCAL over there.
They do a traineeship, but go to school 2 days a week to keep up the basics like English etc.

You may have to trust in the way you have raised her, your partner is right. I would still give her boundaries though. If she gets a job, does that mean she gets to come and go as she pleases? Do the rules that apply to the other kids (like chores and curfews etc) still apply to Ariani?
She will be having more to do with older people in the workforce that have more freedom that she will as a 15 y.o, and that will probably be the next bump in the road.
You might want to tackle this possible issue before it becomes a problem. Getting a crystal ball seems to be the easiest way to do this!!!

Good Luck, it would be nice if she stayed at school, but doesn't mean she can't achieve anything. I left early too, but I'm way ahead of alot of others who stayed and have degrees they will never use.