Is grinding the mesial surfaces of teeth to make room a standard orthodontic practice?

My daughter has had braces for almost 2 years. She is due to get them removed in May or June of this year. I asked our orthodontist if she is on track to have them removed on time, or if it will take additional time. He said her bottom are still crowded. The front 4 teeth on the bottom are still not aligning properly and the orthodontist wanted to grind the mesial surfaces of these teeth to make room for them to align properly. I question whether or not this will damage the enamel. Should a palate extender have been used if there was not enough room in her mouth? Or should the orthodontist be allowing additional time for the teeth to move into position? From what I saw and what the orthodontist explained, there really isn't room for any of her lower teeth to move into position, so they want to make room by grinding in between her teeth - removing healthy enamel - just so her braces will be removed in the allotted time. I am very troubled by this. The assistant said they do this all the time, but I have never heard of this practice and want to know if it is safe, if it standard procedure, and if it will cause damage to my daughter's teeth. My daughter is almost 15.