Helen (write) ......... to me often, but now she phones.
Is it possible to use "would write" in this
Helen (write) .......................................................... to me often, but now she phones.

My book says.
"Would" describes repeated actions in the past, but not states. It means the same as used
to. It is more common in descriptive writing than in speech.
On winter days, we would sit/used to sit around the fir e and tell stories. (action)
I used to own a motorbike. (NOT I would own a motorbike.) (state)"

Question

Helen (write) ......... to me often, but now she phones.
Is it possible to use "would write" in this
Helen (write) .......................................................... to me often, but now she phones.

My book says.
"Would" describes repeated actions in the past, but not states. It means the same as used
to. It is more common in descriptive writing than in speech.
On winter days, we would sit/used to sit around the fir e  and tell stories. (action)
I used to own a motorbike. (NOT I would own a motorbike.) (state)"

Answer

"Helen used to write" is more natural.

"Would" indicates a habit or a state in the past which may or may not continue now.
The focus is on the past.  There is not usually a comparison with the present.
Last year, my brother would walk to work.  (no reference to the present - we don't know if he still walks to work)
Last year, my brother always walked to work.  (no reference to the present - we don't know if he still walks to work)
Last year, my brother always walked to work, but now he drives to work.  (natural - reference to the past and the present)
Last year, my brother would walk to work, but now he drives to work.  (unnatural because "would" is not normally used to show contrast)

"Used to" indicates a habit in the past that no longer happens.
The focus is on a comparison between the past and the present.
Last year, my brother used to walk to work, but now he drives to work. (natural - reference to the past and the present)
Last year, my brother used to walk to work. (but doesn't now)  (natural - reference to the past and implied reference to the present)

Answer

Yes, that's fine.

Take a look at this if you'd like to do some more exercises:

- https://www.examenglish.com/grammar/used_to_would.htm

Hope that helps.