If you can convince your sis to only ever distill her own fragrances and use those, you would be doing us all a huge favour, tbh. Distillation isn't even hard, the scent is often milder and doesn't have a ton of binder, which I think is the part that makes stearing "scented" candles so unpleasant to be around? Burning stearin releases its own microparticles into the air but the particles from the scent oils often don't burn as neatly and are much more harsh to breathe in.