Thanks for the reply! Love your username, btw. Takes me back!
Yeah, Carrie mentioned that she briefly worked with a vocal coach in preparation of TSOM live. But she indicated that the express purpose of the endeavor was to reduce some of her signature country-inflected twang to align more with the vocal style required of Maria. This involves things like reshaping the mouth and refining the articulation of vowels to influence the tone and enunciation/accenting. So, sadly nothing that would have changed the course of her actual vocal delivery beyond this context.
As I've discussed many times on here, the thing that would be most valuable to her is working on strengthening the transitional points in her range where the placement of resonation shifts. It's about developing the ability to sing through those areas without breaks, cracks, and undesirable changes in tonal quality. To achieve this, you need to coordinate your breath support, vocal cord tension, and resonance adjustments as you ascend or descend through the passaggio. This allows a singer to expand their range and maximize the quality of production at both ends of it. Carrie will NEVER do this because the only way to develop this technique is through repeated exercises and scales that strengthen these muscles gradually over time. It has a cumulative impact. Carrie openly talks about not doing warmups (I mean, what warmups can one possibly do if they refuse training and don't have the guidance on what specifically to do anyway?) even before shows. You really think she's going to sit there practicing scales using these modification technique on her own time? Will never happen, unfortunately.
At the beginning of the CP era, she spoke about it:
However, she did not hire a vocal coach to make sure that her voice was back on par for the record.
She revealed: “No, the only time I have ever sought a vocal coach’s counsel was when I was doing The Sound Of Music, and that was because it was a completely different kind of music and I wanted to be respectful of what I was singing, as much as possible and try to get some of my twang out. But not during anything else. I feel like you just kind of have to find your way through it. I don’t like it when people try to tell me how to sing, because it should be natural.”
Source:
https://www.vulture.com/2018/11/carrie-underwood-interview.html