What she is experiencing may or may not be implantation bleeding.
Some people experience this bleeding, some people don't. Some people have morning sickness, others don't.
Please don't use spotting as an indication of pregnancy, the only accurate ways to find out if your girlfriend is pregnant is to take a pregnancy test or wait 9 months. According to our Pregnancy Risk Assessment Chart, you have a high risk of pregnancy, so it's best that you take a test as soon as possible rather than relying on signs which may not be there.
Pregnancy tests are accurate from the 10th day after the incident, or from the first day of a missed period. If you go to a planned parenthood center/GP, see about getting a full STD screen for both of you at the same time, because unprotected intercourse carries high risks of contracting STDs and STIs. Most PP's and GP's can give you a prescription for cheap condoms and advise you on birth control methods as well, so take advantage of this and look at your options for the future.
[This message has been edited by entropie (edited 07-17-2002).]