“MIRACULOUS usually refers to an individual event which apparently contravenes known laws governing the universe, ex: ‘a miraculous answer,’ ‘a miraculous success’
-performed by or involving a supernatural power or agency: ‘a miraculous cure’
-of the nature of a miracle; marvelous
-having the power to work marvelous, outstanding, or unusual effects: ‘miraculous drugs.’”
(Webster’s Encyclopedic Unabridged Dictionary of the English Language)

Because the adjective ‘miraculous’ is not usually used to describe people, I’d like to suggest that, although the Virgin Mary is believed to be a holy figure, it is her statue, in this case, that holds these special powers, and is able to cure the sick, or perform other miracles.

miraculous does not only carry the message of causing miracles.

Collins dictionary explains:
1. of, like, or caused by a miracle; marvellous
2. surprising
3. having the power to work miracles

Besides, neither Collins nor Longman Dictionary of Contemporary English differentiate use of the word for persons and for things.

See the examples of miraculous person in the religious context:

Therefore,
one cannot be a Christian without a belief in Christ as God-Man and in the Church as His God-Man Body, in which He left His entire Miraculous Person. The saving and life-giving power of Christ’s Church lays in the eternally-living and all-present personality of the God-Man.

from: http://www.decani.yunet.com/papism.html

another example would be:

Having come to learn that Jnaneshvara, though a young boy, was recognised, along with his two (elder and younger) brothers and the youngest sister, as a saintly and miraculous person, decided to meet them all.

from:
http://www.here-now4u.de/eng/jnaneshvara_s_cangadeva_pasast....

Everything boils down to the question, whether it is the statue that is miraculous = marvellous/holy, or the person...

From the expression you give, Mike, it is clear that it is the person

FIGURA CUDOWNEJ MATKI BOŻEJ = STATUE OF THE MIRACULOUS MOTHER OF GOD

If it was the miraculous statue, the expression would go like this:
CUDOWNA FIGURA MATKI BOŻEJ = MIRACULOUS STATUE OF THE MOTHER OF GOD


It is true, that

Miraculous Statue of the Mother of God

is a more common expression, and easier to find on the web. (See the link that I provided in my first answer.)

However, my guess is that your expression is about a MIRACULOUS PERSON, not miraculous statue...

Hope it helps, Mike

The figure of the Miraculous/Holy Mother of God

I guess, it is "figure", not "statue", since it is heading on a lithograph

Interesting discussion... A similar question is the difference between Protestant and Catholic beliefs. For Protestants, wine symbolizes the blood of Christ, for Christians it IS the blood of Christ. In the case of the statue, this could be interpreted either way.

When looking for the phrase “Cudowna Matka Boża” in Polish, most of the web pages I found were referring to some sort of a statue, or a figure, or a painting of Mary. In Poland it is common for cults to form around such objects, which exist in various churches at different locations. When people pray to Mary addressing her as “Cudowna Matka Boża Zawadzka,” or “Cudowna Matka Boża Przeczycka,” they are worshipping the statue or picture particular to their town.

In English I have never heard of an actual holy person being described as “miraculous,” but what do I know? I have not been to church in many years. The use of “miraculous” to describe people is archaic, at best, but who can be certain now that it was ever “correct”? “Cudowna” could also mean good and beautiful, as well as heavenly or wonderful. And for example, describing Mary as the “Exalted Mother of God” is more common (on the internet) than as the “Miraculous Mother of God” (and those examples do usually refer to statues or figures as they do in Polish.)