A lot of it may depend on how much her personality changes when she's high, and if you are equally in love with her high self and her not high self. Also, if the core aspects of your relationship and your bond have continuity - are still there whether she's high or not - seems to impact the cohesiveness of this type of unequal relationship. It seems to me that healthy relationships are built on honesty and communication, so whether you can stay together is only half the question, the other half is whether you can stay together and be completely honest with each other. If staying together requires less than full honestly, then how together are you? If you both want to be together ignoring this discontinuity and you are equally content with that, then you're good to go -- because in the end, as long as you are both satisfied with the inevitable imperfection of your relationship, then it can continue.
Another thing you can look at, if you want to go there, is why does a person get high every day, several times a day? That's a rabbit hole you might want to jump into or you might want to avoid. Living with a person who is high because life is stressful and this makes it easier to bear, is one thing. Living with a person with serious unresolved issues that is using pot as method of long-term denial and avoidance, that is a person who can be sitting next to you on the couch, but they are not really there.
My wife is high 90% of the time when she's around me (the only time she's not high, is when she's at work). On non-work days, she's starts before her morning coffee and is various degrees of buzzed all day long. I only very rarely get high. I have watched my wife closely, and in the end there definitely is a difference in her personality while she is high, but the change is not really any greater than the general mood swings or perspective changes that anyone goes through in an average day or week. Yes, her mood changes are induced, but her core nature never changes, only some of her rough edges seem to smooth out. Would years of therapy be a better solution? We'll never know, so my personal answer to your question is; I respect and love this person for who she is, and I accept that smoking pot is a big part of it. It's all a package.
Life is inherently incomprehensible, as we are living beings who have evolved with a capacity to conceive of questions, whose answers are unknowable to us. So we live at the edge of insanity all the time, it is the underlying core of every conscious moment. In each moment of every day, we are in a constant process of creating a sense of self and a place in the world while unable to fully define the limits of our influence on the so-called common reality, and simultaneously aware of our finite natures (i.e. our own inevitable death). We fill all of these voids in with stories, because that's the best we can do. For some people, this bizarre existence of being a biological creature experiencing sensory input fused with persistent brain chemistry experienced as an emotional component to everything we perceive... is maddening. If getting stoned is what someone needs to do to reconcile the inconceivable predicament we find ourselves in, so be it. It could be worse.
And yes, [last night when I wrote this] is one of the very rare nights during which I partook.
