It's possible that she's worried you're trying to get "too thin." The last time I lost weight, I got a lot of flak for my mom when I dropped below a particular size, and it was because she thought my goal weight was "too low." It wasn't - at goal, my BMI was still 21, and my doctor signed off on my goal - but she'd literally never seen me that small, and we live in the suburbs where people tend to be thicker, so it was jarring to her to see me that small. My guess is your friend already thinks you look healthy, and is freaked out by the fact that you're trying to get smaller, since it looks to her like you don't need to. (It's also theoretically possible that she likes being the only one in the relationship who has an "amazing" body and is threatened by the possibility of yours being as or more amazing, but that doesn't sound likely based on what you've posted.)
It may be possible, as well, that she has past experiences that you don't know about with an eating disorder (either her own or someone else's) and that's why she's overreacting to the notion of calorie counting. I have a dear friend who was anorexic as a teenager, and even after she was recovered and at a healthy weight, she still got flipped out in conversations about calories and calorie-counting for awhile. It was a topic we just had to avoid for awhile.
Regardless of the reason for her response, the solution is simple - don't talk calories with her. Just keep doing what you're comfortable doing, and don't bring it up. I know it'd be nice if you could talk to her about this since you live together, but we can't always get the ideal reaction from our friends and family. Focus on your own journey, and leave her out of this piece of it.
(Disclaimer: I'm taking you at your word here that you're not trying to get overly skinny and your goal weight is appropriate for your height and build. It's also possible you're already truly thin enough and aiming for a goal weight that's inappropriate. If that's the case, her concern is justified, and you should talk with a doctor about what would be an appropriate goal weight for you.)
| current weight: 147.0