Correct option is B
The correct substitution of the quoted words is "will leave her".
Explanation: The phrase "will leaving her" misuses the gerund "leaving" where a simple verb is required. "Will leave her" correctly forms a simple future tense statement indicating a future action affecting her.
Grammatical rule used: The simple future tense is formed using "will" followed by the base form of the verb.
Example: The decision will leave them without support.