I'd say its harmful, I think saying its not is a little like saying that alcohol or, hell even, sugar arent harmful, they all are but its a question of whether or not you think the harm is reasonable or not or whether you're willing to deal with the consequences.
It isn't really harmful at all in and of itself. It is used in medicinal ways, and almost anything can be argued as being harmful. Red wine has high report for being healthy for the body, in moderation surely, but to say alcohol is harmful is to discredit many historical and current uses for the substance. Similarly, fruit is not at all harmful although it contains tons of sugar, and yet diabetics might as well be signing a death wish eating the stuff. That doesn't make fruit bad for you just because it has that side effect. It is people's weak wills and lack of testicular fortitude that are harmful.
Substances and their pros and cons ought to be carefully considered. If prpl didn't have the history she did, and mentioned that this happened, I would be suggesting the same because psychotic breakdowns, even minor in nature, are extremely taxing on the body's physical status, and the hormones released by the body when put under stress does a lot of negative things to one's self. Given that she's on medicines as well aimed to target things like hormone production, anything tampering with that ought to be an out right no-no.
There are some made deliberately to be harmful--cigarettes, meth, crack.. none of these serve any sort of purpose besides complete recreation and purposefully driven addiction. Weed is not one of those things, but I'd still say in this case it should be considered harmful despite it not being a harsh drug on its own.
The suggestion of hookah is also a really good idea, whomever said it! It is an almost social occasion, and it is relaxing and smells amazing. I don't smoke, but I enjoy being around people smoking hookah.
It can be an expensive habit though.. Maybe try smoking some flavored electronic cigarettes until you gain a bit of knowledge and money for something fun like that?