Definitely say goodbye! My biggest irritation after 10 years in childcare is parents who try to sneak off! YES it is harder for you to have to say goodbye, but it is sooooo much better for them to be told the truth. I see kids whose parents have snuck off - they spend the whole day searching for them, mentally or physically, rather than engaging in play. Not engaging in play means that their learning is then impaired. Kids who have had the goodbye usually fuss until the parent is out of sight, then may need cuddles or reassurance for a little while, but eventually they all settle down and play properly, which means they can learn.
When it does come time that she's wailing "Don't leeeeeeave meee!" - make it short, sharp and sweet. Say "I have to, darling, but I'll be back at 4:30 (or whatever) and then remove yourself from view as quickly as possible. If crying makes you stay, then of course they will cry more, because it works! Kids learn this so early, like from 15 months or so. And the more they cry, the harder they are to settle, and again, learning is impaired. It may sound cold, but after looking after tons of kids over the years, the best adjusted ones have been the ones with honest parents who don't prolong the pain.