I respectfully disagree. Imagine the fallout, the possible destroyed relationships!
I know your sister is not a child, but this is exactly the reason why abortion has been made accessible to underage children as well, even without parental permission.
Yes, from a Catholic perspective few things are worse than abortion. But if your sister is having an abortion, how Catholic was she in the first place??
Your sister needs emotional support right now. There’s compelling forces driving her to this decision. Telling her she’s morally wrong is the LAST thing to do.
I understand the baby is important from a Catholic perspective, but your sister is worried about her. What about her??
I do not understand your position, perhaps you are not as clear as you think you are. Everyone who has suggested the OP turn to her parents, has given the proviso that this be done only if there is a good relationship between them.
I don’t understand what you mean when you say : “I know your sister is not a child, but this is exactly the reason why abortion has been made accessible to underage children as well, even without parental permission.” Are you saying that even kind, supportive parents have no place in helping their child deal with an unplanned pregnancy? Girls often fear parental reaction because they have an unrealistic impression about what their reaction will be. That being said, the OP is asking for advice on how to help the sister change her mind, or at least reconsider her decision. Telling her to drop the matter, is advice, but not helpful in relation to what she has asked.
As for abortion being a catholic issue, that the baby is important “from a Catholic” perspective that is not true. Many people of various religious backgrounds, and those with no religious affiliation oppose abortion because they realise that an unborn child is a person, temporarily dependent on another. My husband, who at best is an agnostic, can’t understand the self delusional mindset that allows people to pretend that a fetus is not a human being.
You have also not considered the possibility, that if the OP does nothing, her relationship with her sister may still be destroyed. In a few years time, the sister may regret what she did and resent the OP for not trying hard enough to help her. It certainly wouldn’t be the first time this has happened.
But ultimately, no one, who knows an unborn child is not a clump, but is a living being, can stand back, shrug their shoulders, and say, oh, well it’s not my decision. I would be unable to stand back and watch someone drown kittens, something within me calls forth an imperative to protect life. I stand by my advice to seek the help of supportive adults, who can step in and provide a mature perspective. If the OP just allows her sister to proceed with this termination, their relationship will be tainted anyway.