Plot – a young woman joins a good mercenary company, but after a while the company’s work gets too dark, she leaves and travels on a ship, gets off and travels with a half elf mage who tricks her into fighting in Elven ruins, they kill a lich, she continues over the mountains to a small town, joins semi-religious fighting order there, has another battle in ruins near the town, has misadventures, joins elven woodsmen, eventually becomes paladin, I believe, and finds royal family connections.
https://en.wikipedia.org/wiki/The_Deed_of_Paksenarrion
Sheepfarmer’s Daughter (1988), Divided Allegiance(1988) and Oath of Gold(1989), by Elizabeth Moon. The trilogy is printed together as the Deed Of Paksenarrion(1992).