Girlfriend experiences prolonged tightness after sex

I've recently taken a vacation with my girlfriend which ended up consisting of several days of pretty much constant sex. She was having her period at the time. During the last night, she got unbelievably tight at the entrance to her vagina - it was hard to find the hole even with a finger, and impossible to insert my penis even with a lot of lubrication. She was, however, extremely turned on and very wet. This wouldn't be a problem, but the situation has continued for a few days now - she is still very tight and says that she constantly feels stimulated in her pelvic region. We're both confused and are interested whether or not this is serious. So far there have been no other effects, and she is capable of masturbating without much problem, but the tightness lingers.

Also, she did not manage to orgasm during these several days - could this be her body's reaction to a too-prolonged plateau state?

Thanks in advance,
two confused lovers.