Tax liability for 2018 return and 2019 ES-tax are two different things.  If she has difficulty settling the balance from her 2018 return, she could consider applying to pay that by installments but interest and late payment penalty will continue to accrue.

If she is expected not to have sufficient withholdings to cover the minimum ES-tax payment required but does not make the quarterly payments on a timely basis, she would, unfortunately, be subject to ES-tax penalty.  She should aim to pay what she can, even if late, to mitigate that.  Another possibility is to use the annualization method to compute her ES-tax penalty if her income is not earned ratably through the year.

Given the amount she owes and inability to pay, it doesn't sound like the balance due is from personal income.  It may be a case of her not having enough withheld because she over-claimed her allowances on the W-4?  You may like to help her find the root cause and lessen the impact next year.