A linking verb is a verb which connects two parts of the sentence, and after which needs to come a word, so a sentence ending with a linking verb is impossible, it needs to be completed. The only such sentence is 'She seems worried', because you cannot say only 'She seems', it is incomplete, she seems what? Therefore it is a linking verb. The other sentences are completed even without the word after the verb - Maria's mother called. Maria ate. The doctor will arrive. So those sentences do not contain a linking verb.
