Probably best to talk to a tax advisor-- and I am not one. I think the first time you owe a lot in taxes you are not assessed a penalty (if you keep owing every year, you are). This filing season is also exceptional due to tax bracket changes last year.
I've been trying to encourage her to do just this, but she does not always take my advice. She had her mind set on putting this behind her. She does not always make the best decisions.
She can pay in installments vs the entire sum at once: https://www.irs.gov/payments/payment-plans-installment-agree...