My Best Friend Is Worried That She May Be Pregnant

My best friend is worried that she may be pregnant after realizing that her period is late. She is 24 years of age and this is the second month in a row she is experiencing a late period. She told me that she and her boyfriend had been messing around. Both being naked, he rubbed his penis against her clitoris. She said that pre-c_m was present while he gyrated against it, but there was absoltely no penetration involved. This lasted for 30 minutes. She also remembered feeling pre-c_m in her anus area.
He eventually ejaculated, but it was not any where near the vagina.

I have presented the matter at hand.
Now, what could be the reason for her late period? Or is she experiencing a late period?

Is there a possibilty that his pre-c_m or c_m may have entered her in any way without penetration? And if so, could she be pregnant?

Is it that she is stressing herself too much, causing her to have a late period?

I would like some insight on the implications of a woman's hormones, causing her period to be late?