While this is the agencies responsibility, you must as well make sure for yourself, that this has happened. We are naive in thinking that she will not have second thoughts unless she's been prepared for what is to come. They know her better than any agency or attorney. These are all questions that must be addressed. One of the greatest fears that potential adoptive parents has is the birthmother changing her mind.
Fear can be a strong wall.
Attempt to eradicate your fears of what if and put those fears to use by getting more information, making sure she's received the best of support, and communicating with her about these fears. Know that she might change her mind, this is her right. Prepare yourselves for that. Her changing her mind at this point, is not a scam. If she has received no monetary funds or financial support, this is a decision from her heart.