I hope someone can help me ID this book and the author. I read it a very long time ago (must be about 20-25 years ago) as a older teen or tween and it was in German, but I am fairly sure it was translated from English. I am also fairly sure it was a well sized full novel, but could be wrong with that. I have spent some time on search engines, sci-fi sites and Wikipedia, but to no avail. I think the reason I cannot ID the story might be that I am remembering some parts incorrectly or mixing up books. Please keep this in mind, I know this doesn't make it easier. I used to believe it was written by Ursula K. Le Guin, but going through her titles I couldn't find a match.
Here is what I think I remember:
A planet with grasslands or farm lands or similar. A family clan or similar living in a huge mansion. Quite huge alien animals that are (ab)used as mounts but are actually sentient and I think have some telepathic abilities. Regularly there are 'ride out' events and in one of them the brother or friend or lover of the female main character is killed. The main character finds out about the mounts and sneaks into one of their habitats at night, in the end helps to free them and to change the society on the planet.
I think you can see why due to the female main character and hidden subversity of the plot I thought of UKLG as the author. Again the disclaimer that I might be mixing things up or plainly remembering them incorrectly.
Any ideas, comments or answers are greatly appreciated!