Cap new she can lift this harmer and Thor knew it too,Cap didnt wanna disrespect Thor..anyone who's pure in heart can lift that harmer...Thats why in endgame said "i knew you can do it"
Pretty sure Cap could always lift it, but just didn’t want to make her friend feel bad over a dumb joke. He didn’t need the power, so she didn’t take it. That’s WHY she was worthy.