I am chiming in here. Excuse me if I come on strong about this; I don't know you personally and may express strong feelings about this which are based on my own life experience as a T1 female child.
My doctor was obsessed with weight. He used the BMI chart. I look at pictures of myself as a kid, and I was thin. My mother believed the doctor because where she came from, all doctors were just "experts." I have since learned that this doctor was not healthy and that he did a lot of things that were far from psychologically sound. A lot.
Constant scrutiny is what I went through. I think it was based on fear. I was a young lady, just approaching adolescence, and I was being controlled in every sense of the word. Controlling behaviors and constant scrutiny are demonic in their effects, most especially on a young T1 who is probably already bombarded with unrealistic, cruel ideas of what all females ought to look like. It is humiliating and degrading to any person's spirit to be examined for weight gain day in and day out. My father (whom I love from a distance) subjected both my mother and I to that degradation for years. It is an inherited practice. It also, inevitably, broke the family into pieces.
Why don't you want her to "balloon up?" Do you weigh her every day? Why? If it's doctor's orders, why does the doctor order this? Weight gain and loss happens with T1. BMI is a 19th century artist's (was it artist...CHLjoe can tell you) conception of what people should look like. It has no scientific basis at all. Weight is not magical. It will not prevent (and may, if zealously sought, cause) complications.
I know two T1 women who have severe eating disorders. In both cases, the disorder had its roots in the family dynamic. Every item was evaluated before it hit their mouths: "Why are you eating that! Don't eat so fast!" I don't think there was any lack of love in either family, and I don't think either family wanted their daughters to develop bulimia or anorexia, but it happened.Even after one daughter had been in coma more than once, had serious complications for bulimia, her mother still refused to stop preying on her whenever they were at the table together, defensively lashing out at anyone who questioned this treatment. I don't think her mother could help it; I don't know why she kept on at it. I still don't understand that. This is a diversion...
A doctor is not always an expert. Some are dangerous. I wish this were not the case, but it is. My doctor was "fabulous," I think mainly because he earned a reputation as being a comforting, absolute-statement-delivering messiah, but he was not. His patients told a different story. He was a Father Knows Best for the parents, and a disturbing, terrible person to the kids.
I am relating personal experience. I am not indicting or labeling your situation. Please consider these experiences as worst case scenarios.
In terms of high blood sugars, I feel sick when they're up for brief periods, and ravenous when they are consistently high. Controlled levels were nigh unto impossible when I was ages 8-16 or so; I came out okay, from the A1C point of view.