Q. My half sister who was my mother's daughter lives in... and is gravely ill in hospital. My mother's first husband was an avowed atheist and taught my sister to be one too. My mother became a BT (after divorce) and renewed her commitment to Yidishkeit and kept Shabbos, Kosher and Mikvah all according to Halacha. My sister followed in her father's teachings and denied the existence of G-d. She was however respectful whenever she would visit us in Toronto and did not smoke on Shabbos or turn lights on or off and in general behaved appropriately but always claiming that she does not believe.

My sister married a Jewish man and had a daughter with him... I have a good relationship with her.

My sister requested in her will to be cremated.  My niece at my request spoke with her mom Friday at the hospital asking her to reconsider her decision to be cremated especially in light of my / her brother's pleading objections. My sister is adamant about it and refuses to reconsider. My niece being an estate lawyer works with frum people and is very familiar with these halachas. Notwithstanding, that she plans to follow her mother's signed wishes. My niece is also not frum but has the spark in her.

I asked my niece to text me her assessment of her mother's mental state all her life including when she wrote the will. This is the exact quote:

"I am remembering now that her mental issues were not different than those with physical ailments. She could not help herself"

Please note, this  does not refer to her religiosity but her disposition which tended to be erratic and not clear thinking in general.

My Shayla is: Can my sister be considered to be a Tinoket Shenishbaat to be permissible to sit shiva  and say kadish for or not should this come to pass?

Shalom.

A.  Shulchan Aruch (Y.D. 374: 4) rules based on Talmud (Moed Kattan 20b) that one is obliged to comply with mourning for a half sibling.

However in your case, Horav Shlomo Miller’s Shlit’a opinion is that, although you are not obliged to sit shiva for your half-sister, you may do so if you so desire, including the reciting of Kadish.

If your niece is sitting shiva, and there is a chance that your sitting with her will be influential in bringing your niece closer to Judaism and eventually becoming a Baalas Teshuva. and it will also create shalom bais and peace in the family, It may be advisable to do so.

The Rov added that it is unnecessary to recite the brocho of Dayan Emes or rend your clothing.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a