Step 1: Identify the subject of the sentence.
The subject of the sentence is "Her hair".
Step 2: Determine the grammatical number of the subject.
In English, the word "hair" is generally treated as an uncountable noun and takes a singular verb, even when referring to multiple strands of hair. For example, "Her hair is long," not "Her hair are long."
Step 3: Choose the verb form that agrees with the singular subject.
(1) are: Plural form of "to be". Incorrect.
(2) were: Plural past tense form of "to be". Incorrect.
(3) is: Singular present tense form of "to be". Correct.
(4) am: First person singular form of "to be". Incorrect.
Step 4: Complete the sentence with the correct verb.
The correct sentence is: "Her hair is crisp and black."
$$(3) is$$