Just "not knowing" doesn't matter.  There needs to be a specific reason (such as they changed the rules after the due date of the payment, or something like that).

She certainly has the ability to estimate the proper payments by figuring her income each quarter before the Estimated Tax Payment is due (and uneven pay throughout the year can reduce or avoid the penalty by "annualizing" the income on page 4 of Form 2210).

There is also the 'safe harbor' of making enough payments during the year to equal your prior year's total tax (or 110% if higher income).

Personally, from what you have said, I don't see any waiver of a penalty.  However, as I originally mentioned, if her actual Estimated Tax Payments were at least 80% of her actual tax, she can avoid the penalty by that provision.
https://www.irs.gov/newsroom/irs-expands-penalty-waiver-for-those-whose-tax-withholding-and-estimate...