Final answer:
The correct verb to use in the sentence is 'es'.
Step-by-step explanation:
The correct verb to use in this sentence is es.
In Spanish, the verb es is used to express a permanent characteristic or identity, while the verb está is used to express a temporary state or condition.
Since the verb is describing Ella's characteristic of being ambitious, which is a permanent trait, we use es in this case.
Learn more about Spanish verbs