Erin, I just talked to my husband and he said that since power steering fluid is a petroleum based product, that at the right temperature it could be flammable. But it has to get to a very hot point for it too ignite.
As for the stalking and the harassing, listen to the advice given here, Please. I know how scared you must be having to deal with this and I can promise that unless you do something now, it will only get worse. Suffice it to say I have been there and speak from experience. Making threats to anyone via telephone, computer or other electronic device is illegal and can be prosecuted with jail time attached. Start saving every message, email, voice mail etc now and get in contact with Verizon and see about getting copies of all text messages. They should allow you to do that, as I have had to do this before. You can also get a list of the incoming calls from the monthly statement you receive. The police should be contacted and at the very least, made aware of what these people are doing.
I hope this all gets better for you, Erin. I know you have a lot better things to be doing, as a 16 year old, then having to deal with stalkers and harassers. Take care and keep us informed as to what happens.