The way things are going, pretty soon Margaret won't have to ask God for anything. American girls appear to be hitting puberty earlier and earlier, with the average age of first period at just over 12.3 years as of 2002 -- versus 12.75 in the 60s. (Weird caveat: within ethnic groups the age of menarche has actually remained pretty constant; it's the group that calls itself "other" that shows a "clear downward shift" and thus affects the whole curve.)
In any regard, even this overall change of 0.45 years -- tentatively attributed to certain environmental toxins and increased body fat, both of which can trigger puberty hormones -- is of concern. The earlier you get your period, the more estrogen you're exposed to -- which in turn may raise the risk, later on, of breast and uterine cancers. (See, Margaret? No need to push it.) And in general, it's not healthy for your body to start maturing sexually before it's done with basic growing. (See, Mary-Kate and Ashley? No need to push it.)
(Since you asked, too-early puberty is way more common in girls than boys; with boys, it's much more likely to be caused by a specific underlying disease.)
But now (via Slate), Israeli researchers have developed an implant that could help girls -- some as young as seven or eight -- with the condition rather jauntily called "central precocious puberty." The implant would contain histrelin, a hormone that bullies the hormones that induce puberty into backing off. (Some girls already use histrelin in injection form; those tested in Israel say the implant was a major improvement.) Let's hope it continues to be found safe and effective: clinical trials are currently under way in the States.
Now if we could just come up with implants that clean the air and remove soda machines from schools.