Is this normal for a young girl?!

Yes. It can take a few years for girls to get regular monthly periods after they start menstruating. At that age the girls hormone levels are pretty irregular because of puberty and it just takes a while for things to settle down. Having light/heavy periods or missing them sometimes is totally normal.

edit- I mean it's normal for a couple years after you start though it might not take that long. If she still has that when she's older or her periods bother her a lot [like terrible cramps or really heavy] then she should talk to her doctor. Or if she just has random questions about it.

Similar thing happened to me. I got my first period November, it lasted like one day, skipped December, got it again in the middle of January and i've yet to have one now.

It's going to be irregular and hard to predict for sometime. This is very normal.

If she has only recently started her periods it is completely normal it takes a few months for them to regulate and become monthly . Most periods only last around 3 - 5 days anyway.

Yes, when you first start your period, its very un even and it doesnt always happen instantly ( like one month, after a other. )

Nothing to worry about ... she just simply pregnant.