optimum frame size for very small 5'2" female I have a lady friend who's interested in getting into road cycling. The smallest frame sizes I've seen so far in the market are 48 and, in one instance, a 47. Is this about the most common and/or smallest starting point for frames for these riders? She's average weight (around 100lbs). Any recommendations on frame size would be appreciated.
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.