azncow41 is right, its the conversation after the encounter with Marjolaine that 'changes' her if you tell her that she is a bard and to accept it, rather than any of the more 'sooofteee..." (as she would call them) options.
I didn't notice that many differences in the dialogue after much other than if you spare Marjolaine, you get the option in one of the post-encounter convos to say "I told you that you should have killed her!" or words to that effect. Kind of intrigued as to whether there is any differences further on as this is my 3rd playthrough that I got round to killing Marjolaine, the first two times I let her exit (but still hardened Leliana after). Think on my 4th I'll leave her as a softeee