Asking my supervisor to be frank and give feedback
It seems that you are overthinking this. You say she is like a friend. Neither a friend, nor an advisor, has any incentive to lead you into traps. Accept it if she praises your work. Perhaps you are on the right track after all. 

But we can all improve at the margins, at least. If you have specific doubts about particular things that you do, or write, ask about just those things and listen to the answers. Perhaps there are suggestions for improvement in there that aren't criticisms, but just pointers to better ways to do or say things. 

But, your note almost sounds like you are soliciting negative feedback. 

I'm pretty sure that if a friend and advisor saw you going down the wrong road you would be told that. Otherwise she is wasting her own time as well as yours. That doesn't seem like a reasonable action for an advisor. 

After all, if you finish and go on to a brilliant career it reflects well on her also. Relax.