I think that while one's personality traits may change over time, to want to change one's personality implies a refutation of self, a rejection of "who you are", a denial of what makes you unique, a failure to embrace both your stengths and weaknesses.
Now, there's a problem of definitions, and a lot of times, colloquioal usage of "personality" might encompass behavior that is certainly changeable and indead healthy to change.
i.e. calling someone an a*hole, another a slacker, a third a drone might be construed by some as describing their personality. Certainly, if an a*hole, or a slacker, or a drone decides they don't like what their behavior is getting them in life, they may be motivated to change. But to me, that's not changing their "personality."
Far be it from me to claim much expertise in the field of
Personality Psychology. I'm not a psychologist, nor do I play one on the internet. Although I sometimes
pretend to be a psychic...
As for me, a trait like introversion/extraversion is an aspect of personality, and it's like asking "where do you get your energy from?" In broad brush strokes, if interacting with people, doing activities "energizes you" then you're probably an extravert. If having alone time, contemplating, having quiet time "energizes you" then you're probably an introvert.
As far as I'm concerned, introverts can be very skilled at interacting with people and socializing. It's just that it "uses up their energy" to do this, and at some point, they need to "introspect" and recharge their batteries.
Is it desirable to change this trait? I'm in favor of embracing and accepting "who you are" and figuring out how to get what you want in life knowing your strengths and weaknesses and personality traits.
And I'm in favor of people like lightthecandle ending their "analysis paralysis" and getting out there and taking action to improve their lives.
As for her, while there's many steps that can be taken, I strongly believe that for her, The First Step would be to do some vigorous exercise immediately.