Hello and thank you for your question.
These taxes are generally reported on Form 941, which needs to be filed quarterly. If her liability is $1,000 or less, she may be able to use Form 944 instead of Forms 941.
Generally, she would also have obligations to file payroll tax returns for state withholding, state unemployment, and federal unemployment. In a case where no Forms 941/944 have been filed, it's likely these are being neglected too. State withholding may be reported and paid along with sales tax depending on the state, so there's another thing to consider.
While it's beyond the scope of this question to go walking through all the steps to properly file payroll tax returns, especially for tipped employees because there are additional reporting requirements, I think it's safe to say this person needs some professional help. If the client doesn't want to pay for ongoing assistance with payroll tax reporting, then at least get some help in learning initially.
There is further a tax credit employers can claim for taxes paid on employee tips. It's often missed, fyi.
Most payroll taxes can be paid electronically. To pay federal withholding, social security, and Medicare taxes electronically, your client needs to register at www.eftps.gov. Your client can also use that website to pay federal unemployment tax (Form 940).
I hope this helps.