If you're really stuck,
~Link~ also has a search function where you can imput a meaning and it'll give you all the names in its database that mean whatever word you put in. That's helped me name a great deal of characters. You could search for the meaning of a word that, in your mind, best describes her character.
'Strong' + feminine names gives you:
Arnia, Berta, Bryna, Bryndis, Denim, Drucilla, Gertrude, Gesine, Harding, Hilliard, Iphigenia, Mina, Minna, Passion, Philomena, Timber, Valene, Velma, Wilhelmina, Will, and Zephyra.
You can play around with that, it might help. Or you can get a baby name book and start flipping through the pages until one catches your eye. That's helped me, too.