Peninnah is the "rival" of Hannah (mother of Samuel). She was nasty to Hannah because Hannah had no children. Read it all up here: [link]
I had to think a bit about polygamy while writing this one. What does it mean to be Wife Number Two? What does it feel like to have to share one's husband? I'm sure there must be lots of competition and insecurity involved (one can see that with quite a few OT wives, e.g. Sarah and Hagar, Rachel and Leah, Hannah and Peninnah). I can imagine that Peninnah pestered Hannah not so much out of spite as out of insecurity and wanting to prove herself against the first wife.
Polygamy is no longer so common, fortunately. But I think we can still get into similar situations. Marrying a widower or divorcÚ for instance, and having to deal with the memory of the first wife and all that she could do better. Or being someone's girlfriend and knowing there's still an ex or more out there whom he might just still have feelings for if only she was willing to take him back. Men probably go through such insecurities too, though I guess they react differently.
What do we do with our insecurities? Do we, like Peninnah, try to make ourselves feel better by bringing the other person down? Or do we take our insecurity to God, who knows how we feel and can heal all our pain if we just let Him?
The "sister piece" to this one is, of course, Hannah's poem, The Other Woman
For the Women of the Bible challenge.