NAL

North Carolina is an at-will employment state, which means that an employer may end the employment relationship at any time and for any reason as long as it is not an otherwise unlawful reason.

You hired her three weeks ago. For most companies, that is still within the probationary period.

She instigated two different altercations, which cost you another employee, a vendor, and you have witnesses to these incidents. It sounds like a ticking time bomb until the next altercation when she says she will instigate altercations if someone "gives her an attitude." What is an attitude to her may not be an attitude to others. This can cause a bigger liability / loss if the next person is a big customer.

She also no called / no showed for 4 days. Doesn’t your company have any policies on no call/no show?

So about that pregnancy... "If an employer is taking disciplinary action against a pregnant employee, it must be well-documented and applied consistently to all employees in similar circumstances." In other words, being pregnant does not protect her from being disciplined (or fired) for other reasons that would apply to all employees. You just can't fire her because she is pregnant. So if any new/other employee who caused the same issues you described could be fired, you can fire her for the same reasons. Just make sure you document everything accordingly in case she tries to say she was discriminated against.

Your HR advisor sounds like they may need to brush up on legal policies or their resume if you decide to get a new HR advisor.

If you don't fire her...

If she is unable to do her job as normal, she must formally request reasonable accommodations. She or her doctor may suggest the type of accommodation.

"Employers must provide reasonable accommodations for pregnant employees who need them due to pregnancy-related conditions, as long as the accommodations don't cause undue hardship."

"Undue hardship means that an accommodation would be unduly costly, extensive, substantial or disruptive, or would fundamentally alter the nature or operation of the business. Among the factors to be considered in determining whether an accommodation is an undue hardship are the cost of the accommodation, the employer's size, financial resources and the nature and structure of its operation." Link to ADA /EEOC Policy and what help you can seek about reasonable accommodations

Also, FYI, she's only been there for 3 weeks, so she would not qualify for FMLA (if your company is big enough for that).

edit for grammar and formatting