I myself do not know exactly why they are waiting till the end, but I do know that Trinity is only participating as to find out who is one of the best around before kidnapping them.
She will most likely do so with the help of Marcus who will be keeping track of who's ahead in the competition, you know, via hacking their network system, something he too, specializes in, but unlike Shakila, he uses a gun as well, that, as well as his strength which is a bit stronger than your average person you know, having a large stature sort of thing XD
But yeah, Trinity isn't going to do it all, guns blazing sort of thing, she's going to keep it inconspicuous or however it's spelt you know.