The correct structure is:
* If he is...
* If she does...
Why "be" and "do" are not used:
* Modern English verb conjugation: The verb "to be" conjugates as "am, is, are, was, were" and the verb "to do" conjugates as "do, does, did." "Be" and "do" are not used in the present tense (except in very formal or archaic contexts).
* Grammatical simplicity: Using the standard conjugations ("is" and "does") makes the sentence clearer and easier to understand.
Example:
Incorrect: If he be happy, I will celebrate.
Correct: If he is happy, I will celebrate.
When you might see "be" or "do" used:
* Poetry or literature: Sometimes these forms are used in poetry or older literature for stylistic reasons.
* Formal writing: In very formal writing, you might see "be" used, but it is rare.
In summary:
While "if he be" or "if she do" might seem more "grammatically correct" based on older English grammar, they are not used in modern English. The correct forms are "if he is" and "if she does."