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This is an English YA fantasy novel. It's certainly at least 20 years old and likely more.
The setting is fairly standard medieval fantasy. The protagonist is an ugly girl who has been enslaved by a witch. In her time doing domestic chores she has learned to talk to some of the animals around the house. Eventually she escapes, taking the animals with her - I believe there are four, give or take a couple. One is definitely a fish. She meets up with a knight who has been cursed by the same witch to have armour that will always be rusty. They go on a quest together, with spoiler results that I will add only if necessary.