If I understand you correctly, it seems you may have written the email to both your boss and coworker, without differentiating in any way. If you had for example written the mail to the boss with a cc to your coworker, that would mean that you were asking your boss but only informing your coworker. This is that way I would have done it - because the boss is the one who can say yes or no. The coworker only needs to be kept in the loop but isn't the one who can say yes or no.
Feel free to correct me if I've misunderstood.
Regardless of how you addressed the mail, your coworker - as far as I understand your description - has no say in the matter. Her opinions are just that - her opinions. The only two things that matter here are 1) the (as of now unclear) policy, and 2) your boss's decision.
I understand your impulse to clear your name. I get that it's very frustrating to be accused of trying to sneak in an extra vacation day when you have a stellar record of working from home. But I don't think going at it in that way is going to win you any points. So here's what I would do:
- Send a polite email to your boss and cc the HR person. Say you'd like to better understand the policy, and ask for a short meeting after the holidays.
- Leave the coworker out of this loop - the policy isn't her responsibility.
- Keep the mail as short as possible, and cc yourself as well so you have documentation.
Here's a fast-and-dirty example of the kind of thing I mean:
I'd like to better understand the inclement weather policy, and to that end I suggest we schedule a short meeting at your convenience after the holidays.
I've had good experience with working well from home when inclement weather has made it necessary, and I understand the company's need for a consistent policy. There are some aspects of the policy as it's now worded that seem confusing, and I'd like to understand it. I'd appreciate any clarification you can give me.
This way you're asking for help in a polite and professional manner, not accusing anyone of anything. You're also indirectly pointing out that there are problems with the policy, but in such a way that no one needs to get defensive.
Basically, you're giving them an out.
I'd go in with a smile, and have around four examples of previous situations where permission has been granted at the ready, in case the clarification you're asking for proves hard to get. It can often be easier to discuss concrete examples, and if it's the case that some situations would be handled differently or more restrictively now, they might need help explaining it. Your examples make it easier for them. ("I know that situation X has been fine in the past, but maybe it will be handled differently now?")
Whatever you do, don't lose your cool or defend yourself. Your record speaks for itself, and a polite employee who wants to better understand his company's policies is a good employee.
The alternative is of course to write the whole thing off, look for another job, and assume working from home isn't an option anymore. But I suspect your blood pressure might suffer if you do that! Depends on what you need out of this situation, and only you know that.
Good luck!