Here are some options depending on the context:
Formal:
* Colleague: This is a neutral term used for both men and women in a professional setting.
* Associate: This is a more formal term for someone who is connected with another person or organization.
Informal:
* Gal: This is a casual and friendly term for a woman, though it can be considered outdated by some.
* Chick: This is a more casual and informal term for a woman, but it can be considered slang and may not be appropriate in all situations.
* Lady: This is a polite term for a woman, but it can also be considered old-fashioned.
* Woman: This is the most neutral and direct term for a female.
Alternatives:
* You can often simply use the woman's name or job title instead of a generic term.
* If you are trying to emphasize camaraderie, you could use terms like "friend" or "buddy."
Ultimately, the best way to refer to a female "fellow" depends on the specific context and the tone you are aiming for.