Hello Marina, I have just re-read the text. The only 'think about it' is in the previous unit, and this is a perfect example of where repeating the phrase reinforces what has already been said and implied, so I would have to say that 'think about it' is the perfect translation here.
For me 'ponder' doesn't quite fit the context here. I would tend to use ponder in this context if the outcome was likely to be positive - whereas here the outcome is likely to be negative.

Thanks.
We've had so many "think about", I'd like a change. Would "ponder" do?

Hello Marina- your sentence - 'If we consider this, we'll say no.' indicates: If we say yes to this, we'll say no. (which is a contradiction). In this expression, 'consider' implies agreeing to do something.
My suggestion is: Frédéric - If we think about this, we'll say no.