Is it commont for 10 year old to get her period twice in one month?

Yes. A girl of this young age with her periods already will quite likely be very irregular, even for several years. She may have two in one month, then one next month, then skip three months. Many of these cycles may be anovulatory. It's nothing to worry about, but make sure she is taking a vitamin with iron, as she is likely to get anemic having more than one period a month and at such a young age.