A few things can be said:
-this girl is dishonest and that's a quality that people will not tolerate, which could mean her friendships are put at risk
-the hsc can never be entirely fair. I'm pretty sure there are people who do this or much worse
-what happens after hsc, will not accept anything like this so eventually she will change her ways, hopefully
-you need to stop associating with this person and work on your hsc
-this girl is dishonest and that's a quality that people will not tolerate, which could mean her friendships are put at risk
-the hsc can never be entirely fair. I'm pretty sure there are people who do this or much worse
-what happens after hsc, will not accept anything like this so eventually she will change her ways, hopefully
-you need to stop associating with this person and work on your hsc