-  ‘in a temper’ in place of ‘in temper’.

In the given sentence, there are a few errors in the use of verbs and adjectives, which makes the sentence grammatically incorrect. Let's break down the sentence into its parts and analyze them:

Part 1: "Don't talk to her" - This part of the sentence is correct. The use of the contraction "Don't" (Do not) is appropriate, and the pronoun "her" is also correct.

Part 2: "she always" - This part is also correct. It is a simple subject-verb clause, where "she" is the subject, and "always" is the adverb modifying the verb "remains."

Part 3: "remain in temper" - This is the error part of the sentence. The phrase "remain in temper" is grammatically incorrect. The correct phrase should be "remains temperamental," where "temperamental" is an adjective that describes the subject's behavior.

Part 4: "these days" - This part is also correct. It indicates the time frame for the subject's behavior.

In English, adjectives are used to describe nouns or pronouns, while adverbs modify verbs, adjectives, or other adverbs. In this sentence, the phrase "remain in temper" is incorrect because it uses the verb "remain" inappropriately, and it doesn't use the adjective "temperamental" to describe the subject's behavior.

To summarize, the correct answer is option C, and the correct sentence would be:

Don't talk to her, she always remains temperamental these days.