Hi Rainbow! Couple of different spins that might help come to turns with this issue.
(1) She is not saying, at any point, that she wants to leave. In fact, she seems to be trying to open communication with you? I would say this is a very positive thing. The only thing I would suggest to you is that you NOT shut that communication down by simply saying "I'm not doing this!" This FORCES her right on the horns of the dilemma. (One side being that she shuts down her own poly drive, the other that she leaves you.)
(2) Just because she is saying she might be poly, she is NOT saying you have to be. I know at least one couple that the guy is very mono, and the girl is poly and has other partners on the side. This does not mean that she will EVER leave her primary partner (You). Perhaps discuss this with her, and ways that you might both of you comfortable? (No romantic encounters in your bedroom, for example?) Remember, polyamory isn't just all about sex. Its about the need to open love up. Love is not a finite resource, is our contention.
Communication is key, always.
Have a wonderful, fantastic day.