As a former JW of 37 years, let me explain... This is what I experienced. I was married for just shy of 18 years to another JW. I got tired of his philandering and I went to the elders with what I thought would be proof of his indescretions and cheating. I had phone records, emails, times when he was out of town which corresponded to other evidence... They wanted no part of it and told me unless he came and confessed or I had two witnesses to his acts I would not be granted a SCRIPTURAL divorce. This scriptural divorce was the only way I would be able to date or remarry after the legal divorce was finalized and not be disfellowshipped. Needlesstosay, I called my own judicial committee meeting several months later, after my legal divorce, to inform them that they were going to have to disfellowship me as I had begun dating a "worldly man". Oh and may I add that my ex was the son of a prominent elder... So there's that element too. And nothing was ever done to him. He is in good standing to this day.
So to answer your question, yes a sister can divorce her husband without being disfellowshipped. However, if she begins to date without a scriptural divorce given by the elders, she will be questioned and if she doesn't stop dating or does remarry, she will be disfellowshipped on the grounds of adultery, just as I was.