By "worse", they mean and I know, (my bro is BPI and I BPII) that people that are or have Bipolar-I have more than just "mild" manic episodes and depressive episodes are usually not those risking suicide as with people that have Bipolar-II. And this even is not just a black and white situation, symptoms/traits still can vary patient to patient. But basically, what has been said holds true.
Bipolar-I is a more severe case when referring to the manic side of this disorder, often resulting or having a strong possibility of escalating into violence.
One thing to not forget too, is the intensity of mood(s) can also vary in each individual.
There are several books at the top of all the threads here, as well as some internet info. that can offer more detailed info. if you wish to learn more about this. Also if you are under a pdoc's care,feel free to ask him or her for more info., after all a patient has the right to know about their illness/disorder, and treatment options/meds.
The suggested reading I listed is really informative and interesting. There is so much more out there.
When compared to my brother, and nephew, I sort of consider myself fortunate to be Bipolar-II(mild) and have great results with minimal dose meds.
My brother, having BP-I dxed in the mid 60's has been through some nightmares, and back in the day, experimental meds. My nephew too, has had some really rough times with this (see the genetic linkage here?) both experienced some very vioent manic episodes, requiring police intervention, and hospitalizations. Oh well, I won't keep rambling on, I tend to get redundant, ha!ha!
Hope this helped with some info.

Take care now,
DE


PS
Though your friend may be DXed with BP-I, vs BP-II, she should be encouraged that she still can get proper meds. to keep her episodic free. Tell, never give up, even when times see very trying, it can all work out and things do get better.