It's a masquerade ball. She'll likely still be scarred, maybe even disfigured. Knowing how she loves to party, Adam plays on that by encouraging her to attend in a mask and have some fun with no one the wiser. He will convince her that he has her back and will keep the public at bay. Then he will engineer some way of making sure her disguise fails (I envision him manipulating Fallon or Blake to pull off her mask), forcing a horrified (and tragic) Alexis to flee the mansion as everyone sees what has become of the first Mrs. Carrington. This might be the impetus to send her off-canvas until the new, healed Alexis arrives (I'm thinking in season three).