If it were me, at the first opportunity to get before the microphone, I would tell them that “nothing is more precious than life, including their beauty pagent, and I WILL NOT compromise my principles for personal gain.”
Then I would walk off.
If they choose to do so, the decision and any sanctions against this lady need to go viral and the pageant should be boycotted.
IF not, who are they going to offend but the same people who already consider the pageant to be 'exploitation of women' or somesuch and probably will not watch it anyway.
Then I would walk off.
I agree with everything you said except, "Then I would walk off.". I would say, "I will speak out for life and if you want to stop me you will have to remove me from this pageant." Don't ever walk off because they then have bullied you and they win. Stand your ground. Make them remove you, if they will, but then they become the ones who are forced to demonstrate their aggressive anti life stance and reveal themselves for who they are. When you walk off, you give into them in a different way that isn't necessary, nor productive. Again, when you are right, stand your ground, then you put the ball squarely back in their court and they will have to figure out what to do with it.