Being overweight is not necessarily a personality issue. I have seen many thin, scratchy handwritings from overweight girls and many fat handwritings written by thin girls. So there is no correlation whatsoever.
Articles & Insights into the world of handwriting.
Teenage girls tend to use this style of handwriting quite a lot. It implies that they are very much concerned with their own day-to-day affairs, their emotions, their appearance and their entertainment.