$5 results in $50 late fee

What does your lease say?

There are new laws in place re: late fees. Scroll down the linked NYC.gov page for more info and other links that might be helpful https://www1.nyc.gov/content/tenantprotection/pages/new-protections-for-all-tenants

The lease only says about the rent and did not cover late electric payment. In this case, it is not late, just a mistake of $5 short. The utility bill is to the landlord and no due date.

Then tell her "no".

Appreciate all comments, thank you!
I told her a big NO to $50 fee on $5 short of electric bill. New York Law only allows max 1.5% monthly charge on the unpaid balance on utility, on condition of more than 23 days later than due date. Which is not the case here. I paid the difference right away.