H.W.
You know, I have worked in daycare settings in the past. Child care typically does have an (unfortunately) very high turnover rate,depending on the center. Sometimes a lousy director is hired and makes poor hiring choices; we had that happen-- good teachers found other centers to work at and lesser teachers stayed or were hired. At that time, an unhappy parent approached me and invited me to start a small preschool for her neighborhood, so I left.
At other times, young people are hired on who think 'working with kids will be easy'-- there is a sort of idea that 'anyone' can do child care, and then they discover that there is a lot of grunt work to be done, cleaning and sanitizing, diaper changes or ensuring that all the kids wash their hands, and all of the social coaching that goes with working with youngsters. For inexperienced workers, this may be more job than they thought it would.
I don't know if this is a 'normal' thing. Kids going to high school/college are usually hired as floaters or assistants, but not leads. To me, it seems strange to start in a new room and immediately start changing the environment. That would suggest that either things weren't correctly laid out to begin with or that the teacher was trying to put her stamp on the room right away. More experienced teachers would likely try to help the transition by keeping the classroom environment the same and then talking with the co-teacher about it when she returned. So, it might be worth it to discreetly ask the former teacher what's up. She might give you some insight. I know that when we had a bad director hired on, I was willing to give some observations and insights to any parent who cared to ask. One has to do this fairly objectively and diplomatically, but if you ask some carefully worded questions, you might get the information you are seeking.