Es verdad que ella, a veces, está un poco cansada.
The correct verb to complete the sentence is "está," which is the third person singular form of the Spanish verb "estar" in the present tense.
The verb "estar" is used to indicate a temporary state or condition, such as being tired, sick, or happy. In this sentence, the subject is "ella" (she), and the sentence is talking about her being tired occasionally. Therefore, the correct verb to use is "está," which means "she is" in English.