MDMA and menstruation?

[2muchpain2feel]

SWIM did some MDMA (unsure of exactly how much) two days into her last period and within an hour or so of coming up had stopped bleeding. She had sort of expected it would mess with her period but had expected it to come back within a day or two. It didn't. And her period usually lasts about 5-6 days so it was barely even half as long as usual.
She then did some MDMA about a week before her next period was due and is now about a week late.

Is this 'normal'? I mean, is the lack of period connected to her taking the MDMA or is that really unlikely?

Just wondering whether she should be worrying yet or not.