First of all I would like to offer my admiration for your patience and your energy; I have had the unfortunate experience of people like this but luckily never as close to home. I might be able to offer some advice though…
Herbs are pretty safe, growing them and using them. Maybe not to make incense but growing your own mint and brewing your mother a cup of fresh mint and honey tea to help calm her might work. If your mother likes gardening you can ask her how to take care of your plants and ask if you can grow some simple herbs in your garden or in your room, she would be none the wiser.
Collecting seashells, stones and what not is hardly ever frowned upon or questioned and can all be easily used in ritual work by engraving symbols into them or charging them with wishes and burying them within Mother Nature.
Cooking; if your mom loves to cook or bake you could work together with her, help her make bread for Easter using specific ingredients for Ostara, or make traditional meals with a magic touch. Bake cookies using fresh vanilla to strengthen family bonds, use basil to clear the air after a fight etc. etc.
I hope this helps even a little and I wish you the best of luck.
Brightest of blessings
"If you take a copy of the Christian Bible and put it out in the wind and the rain,
soon the paper on which the words are printed will disintegrate and the words will be gone.
Our bible IS the wind and the rain."