13 year old with 21 day cycle

Hi my dd started her periods nearly 18 months ago & has got into a pretty regular cycle of 21 days. I know this is within the normal range but it does get her down as she is only getting a 14 day break inbetween. Most of her friends don’t seem to have regular cycles yet so get quite a long break from theirs sometimes. Just wondered if anyone else has experience of this & if it is something that might likely change in the next couple of years? I wouldn’t think about the pill at this age but could be an option in a couple of years I guess