Friend had sex day before period and condom slipped inside of her. she took plan b but is now 5 days late with mild cramping, could she be pregnant?

Can she be pregnant?: There is no way to know by the history you describe. Most likely not. But, once a period is late it is time to get the facts and stop wondering. It is time to do a pregnancy test.

Unsure: Sexual intercourse the day before a period starts is not a very high risk time. However, regarding effectiveness of Plan B - it depends on when she took it. Plan B One-Step is up to 89 % effective when taken within 72 hours (3 days) after unprotected sex. It can reduce chance of pregnancy by up to 95% if used within 24 hours.