I feel like there's really two different issues going on here. It seems to me like her comments are focused on being kink which doesn't have anything to do with being poly. I can understand her thinking that someone who needs a certain kind of kink in their relationships is not going to do well with someone who cannot provide that kink. I can also understand feeling that someone who is new to kink could be overwhelmed.
But none of that has anything to do with being mono previously and looking into poly. As long as you're honest with the people you date (something along the lines of "I agree with/am interested in the principles of poly but I don't know how I'll actually react so please be patient." gives them a chance to decide if they want to get involved with you) I don't see any problem with you "trying" poly. We all had our first experience with poly at some point, even if we felt poly before we knew the word. No one can know for sure what's going to happen in any attempt at a relationship, so as long as you're being open and honest and not using people to "experiment" on, what's the problem?
Pan Female, Hinge in a V between my mono (straight) husband, Monochrome and my poly (pan) partner, ThatGuyInBlack