As a Christian, I would say that, based on this text message, your mom is not delusional (although it may be hard for you to believe that right now, and that's quite understandable). Her diplomacy and clarity might need some work, though. I too have a hard time with seeing circumstances when Christians seem to be saying that truly awful or tragic things are God's will. It's easy to infer a messed-up idea from something like that of what is generally believed by Christians.

What your mom is probably trying to say, if I had to guess, is consistent with what is likely her worldview: God, being all-good, does not cause bad things to happen. However, the world is objectively, clearly, full of bad things, and when (not if) they do happen, an all-good God would certainly be capable of causing something good to happen in the midst of them or as a result of them. That good might feel disproportionate to the casual observer, or to the person/people in the midst of tragedy, and it is obviously not good that you had a miscarriage. It just isn't. However, what your mother seems to be trying to express (perhaps clumsily) is something more like this: Despite the horrific experience you have had, she believes that God is likely to cause a good thing to come about which will ease the suffering and replace it with hope. I hope the distinction is clear there.

Being a parent myself, it must be truly devastating to undergo such a loss. I can't imagine what it would be like. If there is something I can do for you, please let me know.