Is there a windfall carryover?

Good day, all.

 

My girlfriend (single filer) makes a good income, but last year her AGI still soared about $50,000 more than usual largely through investment gains. She was not prepared for how much her tax bill would be.

 

I'm wondering if anyone knows if the tax code has a provision that allows filers to spread windfall income over a  couple of years to blunt the effect of an unusually large tax bill. I know they have a payment plan, but I'm talking about something specifically in the law.

 

Thanks...

Henry