I only did this when my two were older and the fastest flow teat wasn't fast enough any more. It did make a hole, difficult to see, but does make a difference when they suck.
At your lo's age I just went up to the next flow teat, and it took only a couple days for them to get used to it coming faster. I wouldn't switch between the two, she will just get confused and that won't help with her intake.
hth