For K entry, which is better for shy girl. She can make friend but definitely not the social queen type. I heard HM lower division is very nurturing, but also very much attracted by all the special activities that all girls school offers. And I am a little afraid of the potential dramas going on among girls. Any opinion would be appreciated! Thanks!

I think you should focus more on the what would be best for your DD's lower school experience and less on the upper school. DC attended a k-12 school that we love but after 9 years, DC switched to another k-12. A 9th grader can travel much further, so school options really open up. Goals change and kids change so it's hard to plan out at k what would be best for HS. At DC's new coed k-12, there are many new girls who switched from SS schools.
Thank you all for the comment! So it is well accepted that ss is better for shy girl than co-ed in lower school?