Salaam,

There are 2 issues here.

One is your resentment towards her using the deen to guilt you over the years which as a result of her perceived actions, now has manifested as anger.

Two is the overly concern for her behaviour and its impact on your parents.

For the first one, you need to deal with your anger or you will only get stressed and more angry. Turn to Allah swt and pray sincerely, spend time remembering Him and do dhikr to help calm yourself down. Understand that we are only accountable for our own actions and not those of others, so focus on yourself and heal the anger within you so you can insha Allah get reward for this and feel better too.

For the second point, what your sister is doing is based on conversations. You have done the right thing to not assume too much and to try and distance yourself from these conversations IN MY OPINION. You did not mention what her response was to your request for her to take calls elsewhere. If she has private conversations in your presence, you could listen to Qur'an on your earphones, leave the room and engage in some other activity to remove yourself from the situation and not feel affected by it so much. Pray for her to be guided and when you have expelled the anger from within, then try to reason with her if this is an option.

The main thing to do is focus on the core problem which is not your sister's actions but their affect on you. Turn to Allah swt. He will always listen to you. You never have to feel like you can't talk to anyone because we are so blessed that whenever we raise our hands and make dua, our Lord hears us and He is the only one who can change things. Be sincere in your dua, remember Allah swt with more frequency. Read more Qur'an to bring peace to your heart and have sincere faith that things will improve.

I hope this helps you cope better and you find peace insha Allah.

Assalamu Alykum sisters,

I'm finding this post after 5 months, hope you will read it, What Sister Amina stated is good and fine; however I'm a bit of a different  opinion about being silent about what is going on around us, of course I like people who mind their business, but when it comes to sinning and wrong doing, we as Muslims are not supposed to hold our tongue, we must advise the wrong doers about what they are doing, because we are orders by our Deen to make (Amer Bilma'roof and Nahi a'n Munkar), and we would be mistaken if we just pass by and keep our mouth shut when something wrong is going on or some person is doing bad things, specially our relatives, as our Deen teaches us that the one/ones who most deserve our good deeds and cooperation are our relatives then the rest of Muslims and at broad all Humans.

Therefore I would advise our sister to talk to her sister and explain to her what path she taking and how it's a sin to do so.....etc, may be she listens, and stop doing that, otherwise Allah will reward her for what she has done....but if she keep silent while her sister doing all that I afraid Allah won't be pleased with that.....

excuse my mistakes I'm in hurry.....