This is a question I have struggled with as well when it comes to the question of "miracles". I thought, "Sure Satan could cure someone, or do something we think is good, if ultimately it drew people away from God. After all, the Bible itself says in the end days the anti-Christ would perform signs and wonders so magnificent that they would almost deceive even the elect. So who's to say that a miracle comes from God or Satan?"
Additionally, a careful reading of Mark 3:25 and others demonstrates that at the time JESUS was speaking in parables. This further complicates the issue. It almost seems like we are back where the Pharasees started, unable to discern when miracles come from God and when they come from Satan.
We must not allow ourselves to stay in such a sorry state. If, in fact, we use what we already know about God (and Satan) the tool we need for such discernment becomes evident. This tool is the knowledge that, by his very nature, Satan cannot perform creative miracles. He can only destroy. Confuse. Befuddle. He can't create. This is actually why the Church investigates miraculous claims so meticulously. Precisely because of the possibility they may be a deception from the Evil One.
Many miraculous healings have been investigated and if there is the slightest explaination that's natural, or even that the miracle itself is fake, it's dismissed. This is why there are so few in proportion to how many are reported. Many more are reported than are validated.
This, that Satan can't create, is just a fact that we all must come to know through whatever means. However it's helpful to realize that sometimes, especially these days, Satan is often thought of as like God just less powerful. This is simply false. There are simply things that he can't do, that God can do. One of these is creation.
He can deceive to make us believe something has been "created" but ultimately this is not true. He can not create.
So let's return to the subject matter here: miracles associated with the intercession of Mary (or any saint). These aren't just "wonders" or "signs", no matter how glamorous or dazzling. The miracles in consideration here are miracles of healing which, at their very root, are miracles involving creation, be it either regrown flesh or disease suddenly overcome. They aren't mere wonders. They are things that require a creator to complete. The Creator.
So this is how we know they aren't from Satan. Because they lead people to Christ AND because, Satan simply can't do them.
Would you call casting out demons an "act of creation" Satan could not do?
The reason I ask is Jesus was confronted by the Pharisees who accused Him of casting out demons by the power of Satan. His answer was:
We do know that Satan's kingdom WILL fall. We also know that he can do nothing that God does not permit in His perfect will and that whatever Satan does it is intended to drive people away from Christ - whether to false gods, idols or substitutes for the true God. Yet even in these acts, God's will is accomplished and all those He calls will come to Him and He will never drive them away.
The Pulpit Commentary on the similar Mark 3 passage (parallel to Matthew 12) has this interesting thing to say about that:
Even him, whose coming is after the working of Satan with all power and signs and lying wonders, And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved. And for this cause God shall send them strong delusion, that they should believe a lie:Also remember that Jesus said this deception coming would be so powerful it would deceive even the elect, if that sort of thing were possible (by inference it is not),
(2 Thessalonians 2:9-11)
For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect.So now we have no ordinary roster of signs and wonders. We have a delusion, sent by God, that will allow the great deceiver to fool everyone but the elect. This means any of the easy tests we might come up with, however reasonable they might seem, could fail. By definition, it will be impossible to see through this deception by ordinary human means. God Himself will preserve those who are His elect sheep. They will avoid deception, not because they are smart, or have used readily available "miracle" tests. They will avoid deception because they are elect, and as the elect, they have an indestructible love of God's truth.
(Matthew 24:24)
Trust in the LORD with all thine heart; and lean not unto thine own understanding. In all thy ways acknowledge him, and he shall direct thy paths.Peace,
(Proverbs 3:5-6)