No, it’s not howdy. You don’t hail your average person, much less announce that they are “full of grace”. That whole sentence is full of profound meaning. That is why she is amazed and not terrified like everyone else who is greeting by an angel.
Okay. Let's go back to Scripture. And, full disclosure, I erred when I said it was from Luke 1:26. It's Luke 1:28. Here we go.
Go to biblestudytools.com to help with the original language: https://www.biblestudytools.com/kjv/luke/1-28.html. Notice I have it set to look at KJV because there are tons of reference tools from that translation. When you pull up that Bible verse, if a lot of the words don't have links in them, click on the Settings gear and turn on the Strongs numbers. That'll make many of the words appear as links (which corresponds to the English words that have corresponding Greek words). The English words without links weren't in the Greek manuscripts, they were added later to make the English more readable. (In other words, it's probably best not to infer doctrine or theology from English words not based on Greek from the Scripture manuscripts.) https://www.biblestudytools.com/lexicons/greek/kjv/chairo.html to describe the Greek word "chairo". Which it describes as:
to rejoice, be glad
to rejoice exceedingly
to be well, thrive
in salutations, hail!
at the beginning of letters: to give one greeting, salute
That doesn't sound like venerations to me. That sounds mainly like "greetings" or "howdy", not "majesty" or anything like that.
Why does Gabriel tell her not to be afraid?