I don’t know how your sister’s husband is being abusive. The term “abuse” can cover everything from constant criticism to murder. She needs to educate herself at the very least on the cycle of abuse (honeymoon—tension—explosion—apology—honeymoon) to be able to discern what is happening, if things are at the emotional end of the spectrum. If things are, or have gotten, physical, she needs to ensure her safety.
Most marriage counselors will not counsel couples where abuse is occurring. The reason is obvious–when grievances are aired in sessions, that puts the victim at greater risk after the session. But if abuse is happening, she needs counseling on her own, in terms of how to put it to a stop.
There are two separate and distinct issues–civil divorce, and the freedom to get married.
Someone who is in physical or psychological danger from an abusive spouse is not required to stay there and continue to be in a dangerous situation.
Whether you should counsel your sister to divorce her husband is up to you, and what action she takes on that advice is up to her. Right now, the priority should be her safety (psychological as well as physical,) and since we are all duty-bound to take proportionate means to preserve our lives and our health, divorce may in fact be her long-term option. Realistically speaking, her freedom to marry after this nightmare is over with is not the priority right now: You can’t remarry if you are dead.
In order to take measures to improve her safety, she needs to get educated on her options to put a stop to the abuse. A very good resource is your diocese’s Family Life office; the US Bishops’ Council has issued a position statement and a directive to all dioceses to put into place ministries to abused spouses. Additional resources are: Your county’s social services office, the county district attorney’s office, the Legal Aid society, and in cases of real emergencies (i.e., she just got punched in the face or something similar,) your local police department. If things have degenerated to the point of physical violence, she needs to construct a safety plan and be ready to roll at a moment’s notice.
If you live near her, help her amass a stash of clothing, toiletries, money, keys, important papers and lists of documents (e.g., bank account and credit card numbers, etc.) in the event that she needs to make an escape in the dead of night. She will then need legal assistance to extricate herself from this situation, and move on with her life. In the US, a marriage tribunal will not accept an annulment petition for investigation until after a civil divorce is final.
There are a lot of pitifully misinformed and downright dangerous misconceptions about what the Church actually teaches about the permanence of marriage, including the following myths: 1 You have to stay in an abusive marriage, and 2. You are automatically excommunicated if you get divorced. Neither one is true. If your sister has misgivings about taking action based on what she thinks the Church actually teaches, she needs to make an appointment with her parish priest and run this by him.
A divorced Catholic who was in a presumably valid marriage is merely required to live chastely, meaning not cultivating a romantic relationship, having sex with, or getting married to someone else, unless a declaration of nullity is obtained. The divorced Catholic in other words lives in the same chastity that a single person would be living in (minus the freedom to pursue a romantic relationship.) You can be, in other words, divorced and still be a godparent or confirmation sponsor, you can receive the sacraments, etc, etc. You just can’t get married to someone else unless and until you get a declaration of nullity. You can’t date someone with a thought of marriage down the road, and you can’t have sex with someone other than the civilly divorced ex-spouse.
Even the Church can’t dissolve a sacramentally valid marriage, but it can investigate to see whether the terminated abusive marriage was in fact actually a sacramental marriage in the first place. That means looking back (usually, with witnesses,) at the time the marriage occurred, to see if the marriage was sacramentally valid.
In my diocese there is a tribunal lawyer service to help people through the annulment process (obviously, there is a charge for this service, and it is not required by the tribunal.) However, the website is quite educational. One thing was noted on it concerning abused spouses: Frequently, before the time of the marriage, the abuser displayed warning signs that were missed or minimized by the victimized spouse, and that these, if documented well and supported by witness testimony, are quite supportive evidence that something in the abuser’s personality made him (or her) unable to validly contract marriage in the eyes of the Church. But of course, all that is further down the line: Your sister needs to be safe, first of all. And the Church does not insist that she remain in a dangerous situation.
I will keep you and your sister in my prayers, and I hope that she is safe.