Hi:) So My Girlfriend And I Had Sex The Day

Hi:) so my girlfriend and I had sex the day after her period, but the condom broke. I ended up ejaculating in her. We went emediatly to Walmart and bought plan B, and she took it right away. So at most on hour after inter course. That same day she experienced heavy bleeding about 2 hours after for a while and then normal flow for the rest of the day. The next day it stopped however she has experienced slight spotting ever since. Today is Tuesday, she was supposed to get her period yesterday. She leaves for Costa Rica on Saturday for a week. We really want to know if she's pregnant or not so we can take the right measures early. If she takes a test on Tuesday would it show up? What are the chances of her being pregnant? Thank you so much!!! I'm freaking out.