By all means confront her, just beware you're opening up a whole frickin can of crazy.
Sounds to me, she isn't all that stable to begin with and you're going calmly confront her about her "little ruse?"
Can you talk to your brother about this? Will he see beyond his willy and look at the situation calmly?
My experience in matters like this that keeping my mouth shut does wonders. You start throwing around notions about her pregnancy saga....well good luck there.
You're just going have to ball it up and stuff it down deep in your gullet. People like to make their own mistakes and no amount of talking (no matter how much sense it makes) is going solve this.
You're brother will come round; they all do; too bad it'll be too little too late.