She told KCRA she was in disbelief when she saw that authorities were pursuing the case.
"I actually consulted with the other attorneys in my office to make sure that I wasn't missing something," she told the news station.
Still, prosecutors stood by the arrest in a news release Tuesday, saying that Schwab's blood was not tested for all illegal drugs, and the officer who arrested the 36-year-old is "qualified as an expert in (drug recognition evaluation)" and determined his level of sobriety based on her training.
Solano County District Attorney Krishna Abrams told KCRA that although prosecutors lack a positive drug test, authorities are convinced Schwab was under the influence of a drug that was not tested for at the forensics laboratory.
"This is a case without a blood result, so it makes it a very difficult challenge to prove in court," Abrams told the news station.
Schwab is expected to face trial Jan. 11.