I think if she has requested it not be discussed then maybe it's best to leave it.
Bringing up that your thinking of her at 'this time' might only draw more attention to her that this was the month her baby should have been here. IYKWIM
Maybe if she seems down you could ask if she's ok in passing and just let her know your there if she needs a chat, without discussing what you think is the issue.

Others who have been through this might have more of an idea though. and she's lucky to have you as support.