If a woman were being forced into an arranged marriage she doesn't want, I would not say "congratulations".
If a woman were marrying a man that she chose to marry and was happy to marry, I certainly would say "congratulations".
The difference is that the woman is happy/excited about the situation she is in, hence congratulations are in order. If she is not happy about the situation it wouldn't be appropriate to congratulate her.
Another example:
Woman A has been ttc for quite some time and gets her period. No congrats for that - af is just a reminder that she is not pregnant yet.
Woman B had a condom break and took the morning after pill but is still worried... until the day her period comes. She is happy and rejoices that af has arrived - congratulations are in order.