Rachel, 18 is also the age to volunteer at my shelter. That means you have to be 18 to volunteer without someone supervising.

I shaperone 3 kids ages 10, 12, and 16 every week. They want to volunteer but need an adult to be around. See if someone can shaperone you.

The other ideas that pupper lover and lovemymaltese gave you were great. perhaps you can make some treats and take them to the shelter. Tennis balls are a great toy for dogs too. See if your high school tennis team can give up their old balls. My tennis team did that when I played in high school.

I wish you the best of luck. What you are doing is a great thing. I hope you can get more support from your parents.