I am not clear on what is causing your anxiety on the job, but, if you need to stay with this employer, can you simply transfer to another department?
If NJ has a mandate to offer infertility coverage, then wouldn't you get that coverage even if you left this job and found another, assuming you stayed in NJ?
Would you consider doing an IVF cycle in another state that does not have an age minimum for donors so that your niece could cycle now? You could freeze all the embryos for transfer later if you feel you are not ready to get pregnant right now. I know fresh transfer is better than frozen, but frozens do work and you have many factors to consider that could make waiting and using frozen embryos a wise decision.
If you did a cycle out of state, would your NJ insurance still cover the procedure, or do you have to see a clinic in NJ?
If you felt you just had to quit your job, do you have the option of COBRA, where you pay the premiums and maintain your same insurance? I am not sure what the laws are now but when I went on COBRA, it was available for 18 months after leaving a job.