I seem to be spending the day evading a colleage's emails asking me if I've done a piece of work she asked me to do yesterday.

My reasons for this are

a) I've done it.
b) In three years of working here I've never not done something someone's asked me to do so I've got no idea why she's asking
c) It isn't really that important.

But nonetheless all I have to do is email her a polite "yes, I've done it". Instead I've managed to not answer all morning, then when she emailed me again to chase up, emailed her back to apologise for not having had time to reply to the first email but still without actually answering the question.

I'm chasing a promotion soon and, if I don't get it, leaving my job so I've got every reason to avoid pissing people off for wanting a promotion/reference-based reasons so why the fuck can I not just behave sensibly?