I'm not a doctor, but I do know this, 36 days is NOTHING to be concerned about. I've gone 3 months with out a period, and I've also had one every 2 weeks for 4 months. A girls cycle depends upon a lot of variables including stress levels and physical fitness.
You would be amazed to know that even if she ISN'T feeling stressed out, her body could be reacting to the stress that is held in, in other words she doesn't feel it but her body does.
Or it could be that she just needs to be put on BC and get her period regulated. Mine regulated itself after I got out of my stressful situation.
Hundreds of things can cause a missed period. First i suggest she take a home pregnancy test, because it is theoretically possible to get pregnant without penetration. (Very unlikely, but in theory it's possible.)
Also, do you know if that's normal for her? Not every woman has a 28 day cycle. If she has irregularities in the past, I suggest she bring them up with her gyn. Irregular periods CAN be caused by medical problems, so it's best to have them ruled out.
She might also want to talk to her dr about a regular from of b/c. No birth control is 100% and only condoms will prevent a STD, so still use condoms. But if a condom breaks it's a BIG relief to know pregnancy is unlikely.
Besides that, a week isn't very long to be late. This can be easily due to nothing more than stress. However, if she's put on a lot of weight or lost a lot of weight or her period doesn't come by the end of next week she should make an apt with her gyn/dr to make sure nothing is wrong. For now, no reason for you to be freaked out.