Very few people are actually tone deaf. This would mean she wouldn't be able to tell one pitch from another. How old is your daughter? A six-year old is not going to have the same amount of vocal control as as 16-year old, or a 26-year old. Furthermore, it is really hard to hear yourself when you sing. That's why people always think they sound "different' when they hear their recorded voices played back to them. It also depends on what kind of music your daughter is singing. Certain types of music, such as opera, take years and years of hard work to master. After all, unless one is a prodigy, how well does a 2-year piano student play compared to one who has studied longer? The voice is an instrument to master.
Now, the bad news. There are a lot of really rotten teachers out there whose main interest is making money. They will tell the untalented anything to keep them coming back, and often make extravagant promises like guaranteeing anyone that they can increase their range by two, three, or four octaves using a special technique known only to that instructor They might be people who while genuine in intention, just do not have the knowledge or training to teach other people good techniques for healthy and competent singing. How much musical training has the coach had--a good one should have some sort of formal upper level music education.
Talk to the vocal coach about your concerns. Don't attack the coach, just ask him or her what you asked here, minus the part about wasting money. If your questions aren't answered to your satisfaction, you can take it from there.
Once again, this decision might rest on how old your daughter is. If she is an adult, she will have to be the one to decide (unless your money is paying for the lessons). Good luck
Classically trained singer