Ahhhh, the turn off for you is what you see as weakness. But is she weak or does she not like to argue? Is she this way with everyone or just some people? Have you tried asking her? Next time you witness her agreeing, later when you're alone, ask her about it. Say something like you noticed she was agreeing with so and do about such and such, and is that how she truly feels? Be a safe place for her to be honest. She may have been raised to be nice at all cost, or raised around too much conflict so she now avoids it, who knows, there could be tons of reasons! Whatever the reason, she needs to know it's ok for her to speak her mind.