Question

Mi madre no __________ en el garaje.

Answer 1

I agree with the person above - the correct answer is indeed the word está.
Mi madre no está en el garaje - My mother is not in the garage. 

Answer 2

Correct answer:

Está

First of all, this is a negative sentence because of the use of the word no. On the other hand, está is the conjugation of the verb estar for the third person singular in the simple present. Here this verb is being used as location, because it describes that my mom is not temporarily in a place. Therefore, we can write this sentence as follows:

Mi madre no está en el garaje