Prayer to God should automatically equal worship. The word "pray" doesn't limit to that and never has in old language, including the ancient languages.
Prayer to God DOES mean worship, or at least SHOULD always mean worship. But I think to say "One prays to whomever one worships" presupposes so much fallaciously. Because if someone prays to Mary in asking her to pray with you to God, then it doesn't mean worship of her.
The most common Marian prayer is the Hail Mary -- taken directly from scriptural passages. Neither Gabriel nor Elizabeth were worshiping her, were they?
That is a rationalization only, sadly. What Gabriel said to Mary is not a pattern for us to speak as a prayer. She cannot hear you, nor dos she want to, I should think.
Erecting images that are supposed to represent Mary elicit all sorts of worshipful behaviour. Hence, the danger in creating images against God's command.