No, I’m not talking about your tummy (although it could be that the sentence also applies to that part of your anatomy), I am talking about the middle range of your voice.
If you are a young professional singer and have been taught to “sound good” and aim for “resonance” and volume, you can, especially if you have a good natural voice, get pretty far on not too much skill. In fact, you can actually sound decent, even quite good, and still be over-singing in your middle voice. You can get away with this for a while, mostly due to your youth, but sooner or later you are going to have problems and then things will go downhill in a hurry. This can also happen as a response to repertoire that is dramatic and powerful. It can pull you into a place that is not ideal but one that you can’t fix when the job is over.
The vocal folds will resist a reasonable amount of air being pushed out harder than normal from below by abdominal muscle contraction, and the larynx will stabilize if it’s parked in a “low position” such that nothing much in the throat moves, but the entire mechanism may not hold up well if it is almost always over-stressed. Just because you have strength doesn’t mean you also have stamina. Just because you have stability doesn’t mean you have intrinsic strength. There is a difference and it really matters once your voice is in decline.
Symptoms such as a big, wobbly vibrato, or effort in high notes, or inability to sing softly, especially in high pitches, or needing to use “extreme breath support” or singing slightly flat consistently without hearing it, or feeling like your high voice suddenly “tops out” are indications that your vocal system is way out of balance. Regardless of your teacher’s credentials, it is quite possible that she will miss these issues or blame you or tell you “it’s temporary” or give you remedies that don’t help. Many teachers simply do not understand function well enough to see what is obvious, as their training is largely musical and that is a very different set of skills to have.
It is also true that you can be singing with too much “openness” in your middle voice. How could that be? How can your throat or your sound be “too open”? If all you ever do is sing open vowels at full volume to vocalize and you are encouraged to use a lot of “breath support” all the time for everything, you could still sound very good aesthetically, but functionally, you could be in the kind of trouble I just described.
Be alert to the symptoms I have described and catch them early if they start to develop. You can correct this situation if you get to it before it sets in but if you miss it you can go far down a bumpy road and find it quite hard to come back again.