The difference is that we recognize that she is God’s creation and not a goddess. As God’s creation, we are praising God through her. It’s kind of like when you praise someone’s delicious cookies—you are really praising the chef, because obviously the cookies didn’t make themselves
If you say “those are really tasty cookies” and the chef says “thank you”, it’s not because he has confused himself with a tasty cookie! It is because we really know that we are praising the chef’s excellent baking skills, or what he has wrought. We honor and bear witness to the excellence found in his handiwork
Mary recognized this herself, in the canticle called the Magnificat, where she says “all generations will call me blessed BECAUSE He who mighty has done great things for me, and holy is HIS name”. (The whole of the magnificat is found in Luke 1: 46-55) She clearly recognized that this was God’s work in her, and she is called blessed because of Him, praise be to His name.
Actually, the answers to the very questions you are asking were articulated by one of the greatest (if not the greatest) philosopher and theologian of the Catholic church—St. Thomas Aquinas. Basically what he sets out to prove is 1) honor consists of external and corporal signs that witness to a person’s excellence. 2) it is properly due to those who are above us 3) dulia (an external act of honoring the excellence in a person) is distinct from latria (adoration and worship due to God alone), because the honour due to God is inherently distinct from the honour we pay to men.
The reason that latria is different from dulia is because, as St. Thomas says, “God has absolute and paramount lordship over the creature wholly and singly, which is entirely subject to His power: whereas man partakes of a certain likeness to the divine lordship, forasmuch as he exercises a particular power over some man or creature.” The distinction is manifest on a practical level in that we recognize that God is the author of all good, and all that is worthy of honor comes from Him! For this reason, St. Thomas states that honor towards men can only be paid by means of external, corporal signs (words or deeds or material things), but honor towards God “may consist of the mere internal movement of the heart, for instance when a man acknowledges either God’s excellence or another man’s excellence before God.” (Summa Theologica, Secunda Secundae, q. 103, a. 1). .