I think the putting her into a class where she's more suited might be a good step for now, so that she's not frustrated or falling behind. But I think you should further investigate to see if there is a medical reason for her difficulties.
As other moms have mentioned, ADHD can present more so as inattentiveness than hyperactivity in some children. Along with this can be vocal/oral problems which could explain her speech impairment. Speech impairments can affect ability to learn to read (pronunciation, frustration at not being able to say words, etc.) and ADHD can affect learning skills as well. Zoning out could be inattention from having the disorder. So I would get her assessed for that. At the very least, you could rule it out.
The other thing I would do is video tape your daughter zoning out. If it's kind of a spell that's brief and she looks as if in a trance, it could be that she is having absence type seizures. These are very brief, but kids can have them multiple times a day. It can affect learning for sure. Kids won't remember having them. They usually grow out of it. My niece had these. A doctor should be able to tell you from watching a video if that's the problem. And then you would go from there. I wouldn't let on that you are video taping her - if she's zoned out, she probably wouldn't know, but no need to draw attention to it.
Or she may just be a day dreamer type kid with a speech impediment that can be corrected through speech therapy. And she may need extra help with reading and this could improve along with the speech.
But I would get her assessed and get a second opinion if needs be (lots of good ideas below). Sometimes moving a class is the best thing you can do for a child and it needn't be permanent.
Good luck :)