Wa alaikum assalam
Sorry for the delay
Roman Catholics who pray to Mary will deny that they are "worshipping" her. They instead call it "adoration", “veneration” or some other watered-down terms. However, from an Islamic point of view, WHAT IS WORSHIP IF NOT THIS?
By praying to her, they are indeed, associating partners with Almighty God, and thus become "polytheists" in a practical sense, regardless of their lip-service to "monotheism". This is true even if the person doesn't believe what they are doing is "worship".
Islam teaches that prayer and supplication are the marrow of worship, so if one directs their prayers to an intermediary (even if the pray is "ultimately" meant for God), then they are worshipping others besides God!
The belief that there is only one Lord for all the Universe and that He is the Creator, Organizer, Planner, Sustainer of the universe is not enough because, even those who worship idols, most of them believe that God is the Only Creator, Organizer, Sustainer of the Universe but this was not enough to make them monotheists.
The belief in the Oneness of God requires and includes the belief that NONE HAS THE RIGHT TO BE WORSHIPPED BUT GOD. All the acts of worship should be directed to God, such as Supplication or prayer, Sacrifice, Repentance, and all other acts of worship.
Those who worship the Prophets, saints, idols, angels or animals, believe that God is the Creator who has no equal. However, they associate others in worship with God as partners or intermediaries to bring them closer to God. This is the argument which the idol worshippers of all times, ancient and modern, used as evidence. However, the Prophets came to refute this argument and forbid this polytheism, and to call people to worship God alone with no partner or associate.