Not entirely what I need

I'm a college student, home with my parents for the summer.
I have an older sister who has been somewhat overweight since highschool, and it got worse for a few years.
My mother has never been overweight but was not rail thin either. She has never told us that we need to stop eating and get skinny, but she doesn't exactly know when to stop suggesting that we go for a run, hit the treadmill, maybe not eat a second portion or have a healthier dessert.

When my sister and I were in highschool together, she decided to try Weight Watchers, and I joined to support her in her journey. We both had success for a while, but I think after a summer or so, she decided it was not her thing. (To this day she is still losing weight, but slowly, on her own terms, and still with some self-image issues that she really needs to take care of before she can truly drop below the overweight line.)

As for my mother, she started doing Weight Watchers after she saw our success. (I did it a couple more times, but ultimately decided that I needed to make a lifelong change that did not involve converting foods to points.) She has had great success and lost 10-20 pounds, and is now off WW but still exercising and being conscious of what she eats.

HERE is where my problem enters:
My mother is supportive of my journey and tends not to make such comments anymore because I have such a consistent exercise schedule and food consumption. She does often tell me that I'm doing "such a great job" and that I should be proud of myself.

However, she does not make it easy to keep high self-confidence. I used to way less than her in highschool, and I was not overweight. Now.... she weighs at least 10 pounds less than I, which is a little blow to my pride. To make matters worse, she insists on weighing herself every day and gets upset over fluctuations, even though I remind her that this is water-weight and she needs to weigh herself weekly so as not to destroy her eating patterns. She doesn't listen, and continues to complain to me about those "1 or 2 pounds" that she gains some days. Upsetting, to say the least.

My father and I both tell her that she is now tiny and doesn't need to obsess as much over this stuff, or at least if she does, keep it to herself. I know that even smaller people have health concerns and can worry about putting on pounds, but I know that her mentality is not healthy. She still won't listen.

Also, she's a pretty great enabler, whether she knows it or not. When my mom wants something, she gets it immediately. If she wants coffee and cake, we walk to get coffee, and she suggests what I should eat or what we could share. If I tell her that I want to avoid something like that because it would be too far over my weekly caloric goals, she tells me that it's just one day and we can share it or I can work it off the next day. And I give in, which I know is all on my shoulders, but she doesn't help.

If I try to mention any of this to her, my mother is the type of person to take things very personally. Even if I try to tell her it's not an attack on her, I'm afraid that she will spin it (like she typically does) to be about her, instead of me and my needs, and I won't get anywhere except in making her cry or have a horrible rest of the day.

SO basically, my quest for motivation and support from my mother is like walking on egg shells. Sometimes it feels like she's belittling me and calling me overweight, or the way she compliments me makes me feel like she thinks I should lose more weight. When I approach her, excited that I ran a bit further in an exercise or added more intensity, she says, "That's good! You should start lifting upper body weights now."

That sounds like, "Your arms are flabby. Fix it, like I did!"