Check her correspondence, and cut-and-paste from it.
At least until you are confident that you get her writing style.
Create yourself a library of templates from her correspondence.
Create yourself a listing of her favorite expressions.
If she asks you to write a specific letter to a party and you can't think of a template or an original letter that you can use, ask her if she can think of an original letter she wrote that you can use as a template.
If you are doing cut-and-paste, do it but don't admit to it :)
How you make the sausage and from what ingredients is between you and the wall.
workplace.stackexchange.com/users/16993/Vietnhi Phuvan
Make a draft letter and ask for her opinion.
You are not in her mind, so you have no idea how to proceed yet.
Start by reading some of her writings to get inspiration, then write a first draft.
Review it by yourself, and ask yourself what words she would not have used and what you could improve.
Then you can show her your draft and ask for her opinion.
Take careful notes of her remarks, and re-write the letter accordingly.
The second version should be much closer to what she wants.
workplace.stackexchange.com/users/59994/Thalantas
To imitate her writing style read as much of her writing as you can.
Look for common turns of phrase or idioms that she uses, look for a pattern in first and last sentences of correspondence (problem statement, well wishing, summing up, etc), look at the number and length of paragraphs used, does she commonly use passive voice (starting the sentence with the object rather than the subject).
Someone copying my style for emails would see a common pattern of statement of problem - steps taken - request for action.
Common phrase would be "as your schedule allows", "Let me know if there is anything I can do", and "Please advise".
My emails will contain a lot of passive voice.
workplace.stackexchange.com/users/26235/Myles
Break things down As with any challenging task, breaking things down into manageable pieces makes sense.
It sounds as though your boss puts some effort into maintaining good relationships with her readers.
Look at the following aspects of her letters:
How they start and finish - The opening and closing of letters
set the mood, reinforcing the relationship between writer and reader.
Tone
- How is the language used?
Is it business/professional, or is it open/informal in nature?
Is it buzzword heavy or in plain language?
Structure
- How long are the paragraphs and sentences inside them?
How do sentences typically start (and are parentheses used a lot)?
Use of contractions - e.g. or "for example"?
Aim - Letters are written for a reason.
How does your boss get down to the point and either ask for what she wants, and how does she inform the user of key facts?
How does she get what she wants out of the communication?
Analysing these aspects should help in building a decent facsimile of how she constructs letters herself.
workplace.stackexchange.com/users/None/
Read lots and lots of stuff she has written.
Then try writing something up and ask her to critique it.
After a few rounds of doing this, you should get better.
workplace.stackexchange.com/users/36120/mikeazo
I've been asked to start writing letters for my boss. My boss will then send out these letters with her signature underneath them.   My boss has a particular writing style, and she wants me to write using her writing style. I've never imitated someone's writing style before. Does anyone here have any advice on how to do this?
How to imitate my boss's writing style?
workplace.stackexchange.com
<skills>
workplace.stackexchange.com/questions/80319
workplace.stackexchange.com/users/None/
Read as much of her writing as you can for inspiration and make a list of her favourite expressions that you can cut and paste into your writing. Write a draft letter and ask for her opinion on it.  An important step when trying to imitate your boss' writing style would be to read her previous correspondence for inspiration. From this, you can also try to identify commonly used expressions and idioms or even create a template for future correspondence. Of course, you may also wish to get her feedback on any draft letters that you do write.
Check your boss's previous correspondence and try to identify any particular expressions or features of her writing style which you can use in the future. An important step in imitating your bosses writing style would be to read a lot of her previous correspondence to get inspiration. Write a draft letter and ask for your boss's feedback. If you can, use previous correspondence to create a template for future letters and e-mails.