Re: Moral/ethical dilemma - what should I do?
This is exactly my point. Being aware of and willing to live with the consequences. You don’t care about what others think but OP does not feel that way (see quotes in blue below). Since OP does not want to deal with a backlash from her in-laws and/or her husband, then she should not do it b/c again, SHE will the one dealing with it. And unlike you, she cares about what her husband/in-laws think.
Even if OP sends something anonymously…if in-laws/husband find out that someone sent that information, how will OP make sure that they don’t suspect her? I imagine that the information about BIL’s GF is a family matter and the entire desi community is not aware of it. All OP’s in-laws and husband have to do is think about who knew about BIL’s GF, who knew how to contact’s BIL’s wife in Pakistan, and who is the most likely person to go behind their back. With inside family information like this, it doesn’t take a genius to narrow down the short list of people who would do this and had all the necessary information to carry out the plan. What if OP’s husband asks her directly if she was the anonymous sender? Is she willing to lie to her husband and keep up with the lie for the rest of her life? Is she a convincing liar?
Again, nothing wrong with doing the right thing. But we need to stop pretending that it does not have negative consequences. OP needs to be fully aware of the consequences and be ok with dealing with them if/when they happen.