Here's the breakdown of its function:
* Verb: It expresses the action or state of being of the subject, Rosemary.
* Past Tense: It shows that the action happened in the past (yesterday).
* Linking Verb: It connects the subject (Rosemary) to the predicate adjective (sick), describing her state.
Therefore, the function of the verb "felt" is to show that Rosemary experienced the state of being sick yesterday.