Oh my goodness :'( I'm so sorry for all the horror you've endured! That's awful! I really really hope things start to look up for you very very soon. I'm sending you tons of love, hugs, strength, and comfort. For the smell I would approach it like your cleaning a bathroom. Lots. Of. Bleach. Bleach knocks out the foulest of smells because it has a very strong scent as well. I don't know what kind of upholstery you have but try to find some type of cleaner with bleach that wont discolor things. I'm pretty sure no amount of febreeze or air freshners will be able to take the stench of decay away. You need a type of strong disinfectant. Also the smell will only get worse the longer you leave the body in your car. So try your best to find it and remove it. Once again I'm so very sorry for all you've been through and the losses you have sustained.
Edit: Maybe someone will have a more Eco-friendly/Natural way of dealing with the smell but my go to to knock out something foul is always bleach.
Sent from my iPhone using Tapatalk