It might come as news to you--as it seems to come as news to the rest of /r/relationships--but it is not actually within the power of private people to deport others.

OP's wife and his brother's wife were snippy at each other and engaged in high school bitchy antics toward each other. OP's wife didn't like how OP kind of shined them on even though he criticized them in private, and that the brother and brother's wife kept trying to draw him into a kind of druggy lifestyle, since they sit around smoking pot all day. In other words, the same mix of valid and invalid crap that characterize most feuds in /r/relationships. OP's wife was butthurt over the brother's wife entering some photo contest after she did. She was annoyed about the brother's wife bragging about having a baby on public benefits. There was a host of other minor, petty shit I don't remember.

The sister-in-law happened to be in the country illegally since she'd overstayed a tourist visa. Pot is illegal in OP's country. So one evening brother calls OP to come over, who declines--the subtext OP and his wife understood was that he could come over and smoke pot. OP's wife told him she was going for a walk, but really called the cops posing as a neighbor who smelled marijuana smoke. The cops came over, arrested the brother, who received a fine for marijuana possession. This also brought the brother's wife's immigration status to light, so she was (or is in the process of being) deported back to the Philippines.

OP posted saying he was surprised and disgusted by wife's actions, and the reddit reaction was near-universal condemnation, that she (his wife) was evil, sociopathic, etc.

I hope that's a decent summary.