Condoms aren't 100% effective in preventing pregnancy. I've known several women who have gotten pregnant with condom usage, birth control usage, and diaphragm usage. Have her make an appt with her doctor to verify the pregnancy.
She needs to be sure to follow the test instructions exactly. If someone has a pregnancy test sitting around for a while and reads it past the time limit they say to use (for example, ten minutes), there can be evaporation lines that look like a positive when it is not positive.
This is a hard situation, and question to try and answer. If you are 100% sure the condom was not broken, and nothing spilled out, than you should have no reason to believe you have helped with the conception.
The pregnancy test could be defective. Most tests have a control line, and then the line that reveals the answer. If the control line showed up as normal, than the test should be fine. For verification, she could take another test of a different brand. If it shows up positive, she is probably pregnant. She would need to go to her doctor to verify for sure.
If you read on the condom box it says they are only 97% effective when used correctly.
Make a dr's appointment if you don't think she took the test correctly.