optimum frame size for very small 5'2" female
My wife is 5' 2" and raced elite road for many years.  For her proportions 48-49 cm frames seemed to work well.  Sometime she had mentioned interest  in a smaller frame, but when I looked at how she fit on the bike I think it was due to flexibility issues (at that time) rather than frame sizing issues.

Of course this is one person's experience and therefore not a canonical answer. There are a lot of factors, other than frame size, that govern fit, but 48/49cm is likely a good starting point for someone 5'2".

NOTE: different brands will have slightly different fit dimensions (stack and reach) for the same quoted frame size. Frame sizing is  not standardized.