In manhattan sentence corretcion book, under the chapter modifiers, it is explained that adjectives should follow linking verbs such as feel.
e.g. Amy is feeling well. ('well' is adjective that modifies the noun 'Amy')
But in the same chapter, under the problem set, the following question,
Although the ballerina seems healthily, she feels very unwell and is unlikely to dance well at tonight's performance.
Explanation says "very" (adverb) following the linking verb "Feels" is correct.
I am confused, whether adjective should follow the linking verb or adverb should.
Please advise.