A woman can find out if she is pregnant within 2 to 3 weeks after intercourse. Best way to know for sure is to take 3 separate over the counter pregnancy tests, using the same product. Then the two individuals involved should see an OBGYN (or a walk in clinic will do just fine, and pay in cash if privacy or discretion is an issue) if one of the tests show a positive result regardless if her period does or does not take place the first month she is due after intercourse takes place. The earlier both people are aware of the pregnancy the better. Planned Parenthood is also a great resource and a good place to start. Hope this post has been helpful.
Usually it all depends on the woman, like my step mom started showing in about 3-5months and my mom started showing sooner then that. So it all depends. Unless they take a pregnancy test. Then you'll know sooner :)