Is that legal if they didn't do a field sobriety test, only a Breathalyzer and never read her Miranda rights?

You can still be charged with a DUI, even without a breath test. As for Miranda rights, if you are not being asked any questions (interrogation) then Miranda may not be necessary. I would like to see the police reports because many clients I have tell me the same thing. However, upon reading the reports, I see that they were so impaired that they did not remember.