The command is for us to use the present participle of the verb. The present participle is a verb form in which we add -ing to the verb to represent an action that is in progress. Thus, the only correct option is the last one, "is doing":
She is doing what she was told to do.
The present participle can also be used as a noun, an infinitive, or even an adjective. For example:
That dreadful feeling washed over me again.
Thinking before acting is a must if you want to be successful.
