[Always *]

No. She does not sound pregnant to me. Stress could have caused her to miss the one, or if she has cysts that could have been the problem too.
Stomach pains aren't usually a sign of pregnancy. If she has a history of cysts, she should see a doc and find out if having sex possible ruptured one or something like that, but unless she misses another period/starts having morning sickness or another symptom of pregnancy I wouldn't see a cause to worry about that particular issue