Legal Question in DUI Law in California

They can... but they must qualify as a valid prior. The elements of the out of state conviction must mirror the elements of a qualifying offense in California for it to count.

So - it depends on what state it was from, what specific charge she was convicted of and what the prosecutor can prove. They may see it on her printout, but whether it is a "valid" prior depends.

Her attorney can assess the validity of the prior as well as using any defects to her advantage in trying to resolve the case favorably for her.