"The estimate instructions state that she must pay her estimates electronically."

Thats probably why it wont let you uncheck the box.

The VA state website says this:

Electronic filing requirement

Taxpayers who make estimated tax payments must submit all of their income tax payments electronically if:

• Any installment payment of estimated tax exceeds $7,500 or 
• Any payment made for an extension of time to file exceeds $7,500 or 
• The total income tax due in any taxable year beginning on or after Jan. 1, 2018 exceeds $30,000. 

If any of the thresholds above apply to you, all future income tax payments after July 1, 2018 (beginning with the Sept. 15, 2018 estimated payment) must be made electronically. This includes all payments for estimated taxes, extensions of time to file, and any other amounts due when a return is filed.