Formal:
* Ms./Mrs./Miss [Last Name] (use the title that she prefers)
* Professor [Last Name] (if she holds a professorial position)
* Teacher [Last Name]
* Instructor [Last Name]
* Madam (formal and respectful, but less common)
Informal:
* [Teacher's first name] (use this if she encourages it)
* [Subject] teacher (e.g., "Math teacher")
* The teacher
Other considerations:
* Respectful language: Always use respectful language when referring to your teacher, even if you are talking about them informally.
* Personal preference: Some teachers prefer to be addressed in a specific way. If you are unsure, it is always best to err on the side of formality.
Ultimately, the best way to refer to a female teacher is to use the title she prefers and to be respectful of her position and authority.