Мерилин выглядела виноватой, ещё бы ей не выглядеть так.

вот статья из Longman Dictionary

as well somebody might/may (formal) used to say that there is a good reason for someone's feelings or reactions:

Look up a word starting with D or S for samples of headword or sentence pronunciations on the LDOCE CD-ROMMarilyn looked guilty, as well she might.