She is probably hoping that you will believe her so that she can relieve some of the anxiety she is feeling about doing the ritual.
Rituals are interesting in that respect, they are performed as a way to alleviate anxiety, yet performing them also creates anxiety for some people because they are either embarrassed about doing them or afraid they will not do them correctly and will have to start all over from the beginning.
Your friend is also trying to alleviate some stress that she may perceive you are experiencing; if you were to actually believe that this was her last ritual, then you would overlook it because there would be no more rituals occurring.
However, this is almost never the case, and now she has to deal with the fact that she made a promise to you that she will probably not keep, which can create more stress for her and make it even more likely that she will do more rituals in the future.
Any time you see a friend performing a ritual, let him or her know that you are aware of it and that you would be happy to help them seek treatment.