It probably still won't show up on any tests for a couple of weeks though
No not really. If it was around the time she was due for her next period I'd say yes, plenty can cause an abnormal bleeding. But random spring inbetween is most likely implantation bleeding
She has textbook implementation bleeding signs going on. She only bled for a couple of hours the other day, no bleeding since and it was very light colored. There's nothing else that could really cause that is there?
There is a chance. Ovulation doesn't always happen on the exact day it's supposed to but the chances of sex leading to pregnancy on the day of ovulation is small it's the few days before that your much more fertile. Also implantation can occur at day 6 but not often. It's usually closer to day 9.Between both those facts and the fact that you withdrew I would put my money on she isn't pregnant, but it still is a possibility.
Could be, no way to know until she misses her next period and takes a test. If you don't wish to be a father perhaps next time use protection