In the past employer withheld NJ Taxes so we filed NJ-NR, but not 2018. Wife works in NC for her convenience, not convenience of employer. They let her move away but wanted her to keep working full time for them, which she has. She goes up to NJ 2 times a year for a few days for in person meetings. None of her income attributable to NJ except that the company she works for is located in NJ.
New Jersey is one of five states that treats a telecommuter working from a home office on behalf of a New Jersey company to be working in New Jersey. So NJ will treat her income as NJ income.
She should request that her employer start withholding NJ taxes again. You should prepare the NJ NR return first so the software will calculate the credit on your NC return for the NJ tax.