Even before your first date, you knew your girlfriend was a werecow, she put it right up front in her dating portfolio. A bold move, she said she didn't want there to be any confusion at all on the subject. Even so, she'd run into plenty of issues before...people don't understand quite what to expect. Some refused to ever go near her after dark (it's a full moon only thing) or expected exciting, wild prowls through the wilderness (she's a cow, genius, not a wolf).
You figured her out pretty quickly, and she said that's what she likes about you. She goes mostly cow but with some human characteristics...she's still in there, it's just that she's very much a cow and can't really speak. You've spent some nights brushing her fur and feeding her carrots, which she was very appreciative of in the morning. She just wants to be acknowledged for who she is, in whichever form she's in.
One night she kept presenting her backside to you, and you were pretty sure you got the message, but weren't sure if "she" really wanted it. She was a bit miffed the next day and demanded to know why you didn't take her up on her offer...so the next full moon, you went ahead with gusto. It's become a bit of a routine now...