My half sister is not my mom's daughter. She is my dad's daughter from his remarriage after my mom died. She's 20f and I'm 30f. She's getting married in a few months and asked me for the veil for her wedding day. She told me she thought it would be nice to have something borrowed, and to maybe start a tradition of passing it through the family.
I told her I wasn't comfortable with her wearing it since it was my mom's veil, since she's not my mom's daughter or stepdaughter. She told me she's still my sister and I should see it as sharing an important and sentimental piece of my wedding with her for her wedding. That I would get it back that night if it was important but it would mean a lot to her.
It still didn't sit right with me so I said no. She asked our brother (my full, her half) and he said he did feel that way and he didn't think mom would have liked to see her wear it. He also told her mom would have twisted in her grave if we did give it to her after her mom tried to commandeer it when she married our dad and given she never got over that, she'd probably try to wear it as well.