This thread kind of veers off topic early on, but there is an important message here, anyway. This message goes out to all women, but young women especially- showing cleavage is never professional. It doesn’t matter if you are young and hot (you will still be hot, even without showing cleavage) or old and past your prime, cleavage isn’t professional.
I know that some women are larger or higher busted and that sometimes clothes that fit other women with no issues will still show cleavage. That doesn’t matter. You must dress for your body. Camisoles and layers are your friends.