Maybe the next time you have to drive it to and from work, you should put things into perspective for her. For this to be successful, you have to be completely and utterly shameless.
"This week, I burned about $65 of gas. Do you mind if we eat in this weekend? :o No, no, pizza is too expensive. :unsure: I'll just have a glass of water. Thanks."
You could take this as far as your imagination will go.
Then, when she's just about ready to explode and tell you to kiss off, ask her if maybe you could replace the van with another hybrid? If you're feeling especially generous, you could offer to let her pick out and drive the new one, and you'll be happy to just keep driving your old, "used", HCH.
I'm here for ya if you need any coaching or encouragement!
You laugh at me now, but I assure you, you'll be laughing last when you put that "for sale" sign on your van. Gifts won't be necessary; just your gratitude! :lol: