Where to start.
Well my dear-you start by strengthening YOU. Look at yourself and find your good points-if necessary-ask her what she likes most about you.
Identify yourself (and her) she a dom? you a sub? Sounds like maybe so.
If so-how PERFECT.
Look her in the eyes and tell her you want her to dominate you and you will follow her lead-then obey. Let her take you to a ddsm party as her sub and let her make you do as she wishes.
I say this as you said you like the idea of being poly yourself-I wouldn't say that to Mono for example. But if you trust her-and you love her and she loves you-just do it. Great chance to open up to new things and let her pick them.
"Love As Thou Wilt"