she grazed across the plain, a small filled her nostrils which phrase can replace smell to go v e the sentence a peaceful word
she grazed across the plain, a small serenity filled her nostrils
She grazed across the plain, a small fragrance filled her nostrils.
To find a peaceful word to replace "smell" in the sentence, you can think of words that evoke a calm and soothing atmosphere. In this case, the word "scent" can be used to maintain the meaning of the sentence while imparting a sense of tranquility.
Revised sentence: She grazed across the plain, a small scent filled her nostrils.