LOTR is not set in the medieval period. Its a made up era with made up cultures and made up magic. And if you're going to get all Thermian argument about it, LOTR lore has many female warriors.
The idea that female medieval warriors only exist in fantasy is made up by misogynists to gate keep female representation.
Here is a list of named women that participated in battle. Keep in mind that this is just the tip of the iceberg given the erasure of women in history
Joan of Arc
Eleanor of Aquitaine
Æthelflæd
Artemisia I of Caria
Zenobia
Matilda of Tuscany
Margaret of Anjou
Tomoe Gozen
Grace O'Malley
Isabella I of Castile
Fu Hao
Teuta
Joanna of Flanders
Lozen
Jeanne Hachette
Caterina Sforza
Khawla bint al-Azwar
Lagertha
Sikelgaita
Mavia
Dihya
Isabella of France
If you want women in your fantasy novels, why not - it's fantasy.
Let's be real though - sexual dimorphism is very pronounced in humans, and the women you listed were absolutely the exception. Militaristic societies overwhelmingly used men for fighting, if only because women were too valuable for their ability to bear children.
It's impossible to overstate the importance of women throughout history, but they don't have to have been physically fighting in wars for that to be the case.