I don’t do affirmations or pithy, positive statements either (though my sticker collection might have you believe otherwise lol). I agree it’s possible that your therapist meant how you appear to others/carry yourself influences how others see you, so your self esteem level does show, whether you are aware of that or not.
But I can equally believe she might have said you need to wear makeup/new clothes etc because (misguided) people have said that to me in the past. I think the suggestion to challenge negative beliefs you hold about yourself is much more helpful - when you feel better about yourself everything else should follow naturally.