I'm a man with a very deep voice. Not quite James Earl Jones, but not too far off Michael Dorn. It's comically absurd for me to try to do falsetto. Considering I almost exclusively GM, I need to voice women on a fairly regular basis.
My solution, that seems to have worked since my voice changed in the 1980s, is to
soften my voice. I don't mean that you should speak quieter. I mean that you need to take the aggressive edge out of it. As a general rule, women don't have as hard of voices as men, regardless of pitch. This isn't universally true, but playing to norms (or stereotypes, YMMV) can help to differentiate things. For purposes of this discussion, it doesn't matter whether societal norms drive gender behavior or the other way around; they are what they are.
Also, remember than non-verbal elements make up something like 60-80% of the communication. Posture, tempo, cadence, etc. are all important. More importantly, they're things that you actually
can control. Just be a people watcher. Even if it's just TV and movies, that gives you some ammo that will be effective against your chosen target -- your players have similar frames of reference, in all likelihood. There are a lot of differences and people spend entire careers studying them. Doing a couple quick searches on "gender differences in communication" and "gender differences in body language" turned up a ton of papers of varying length, many of which were pretty short and bullet-point filled.
https://bodylanguagecards.wordpress.com/2012/02/04/gender-differences-in-body-language/ said:
1. Everyone stroke their hair with their fingers – in women, the duration is slightly longer.
2. Men and women will both bite their lower lip in times of stress, lick their lips when sensing dry mouth or attraction, in women though it’s more observable because it is a bit more frequent and sustained.
In men: the signals are simplistic....
In women: Body language is far richer....
http://scholarship.claremont.edu/cgi/viewcontent.cgi?article=1521&context=cmc_theses said:
...men and women view the purpose of conversations differently...
...Women are, overall, more expressive, tentative, and polite in conversation, while men are more assertive, and power-hungry...
...women are expected to use communication to enhance social connections and relationships, while men use language to enhance social dominance...
...women use more expressive, tentative, and polite language than men do, especially in situations of conflict...
...women use less powerful speech: they tend to swear less, speak more politely, and use more tag questions and intensifiers...
... men being primarily goal-oriented and result-focused and women being relationship-oriented...
So, the shortcut is to be more deliberate in your motions when portraying a woman than a man. Choose your words carefully, too. Women rarely cuss like a sailor.