You might be liable.

1.  NJ one bite rule, after one bite, landlord might be liable for keeping the tenant/dog if the dog bite again. 

https://www.ginsberglaw.com/articles/what-is-the-one-bite-rule/#:~:text=The%20New%20Jersey%20one%2Dbite,there%20any%20legal%20recourse%20available%3F

"New Jersey courts have determined that the animal’s owner is not the only party who could be held responsible for a dog, cat or animal attack. A landlord or landowner could also shoulder some of the blame. For example, if a landlord knowingly lets a resident keep a dangerous animal on the property without warning the other residents, he or she may be liable for a portion of the damages."

2.  NJ has no requirement to keep ESA animal, only reasonable accomodate to tenant's disability.  Your tenant might showed you a certificate, but you should ask her what disability she had. 

https://www.nj.gov/oag/dcr/downloads/fact-ESA.pdf

"A request that a housing provider relax its no-pet policy to accommodate an ESA would be reasonable if you can show that you have a disability as defined by the LAD and that keeping the ESA is necessary to afford you an equal opportunity to use and enjoy the dwelling, and the housing provider cannot show that allowing the ESA would be an undue burden on its operations"