I need help understanding this Mandarin statement. 她在用梳子给马梳毛.?

I’m a Taiwanese, as a English learner, I also have a lot of troubles understanding the grammar issues, you, native speaker, seem never need to learn.
He is using a brush to brush the horse's hair” is the perfect translation of
“她在用梳子给(她的)马梳毛”. If “她的” is added in this sentence before “馬”, which would mean clearly, that the horse belongs to her or is temporarily under her control. But actually to add or without adding “她的” in this sentence, the meaning of the sentence won’t change a lot, or say this way, still the same.
In sentence - “她在用梳子给她梳马的毛”, there are three illogical points, the first one is “給她梳马的毛/她梳马的毛”, if this phrase is normal, its meaning will become, “毛” belongs to “給她梳马 or 她梳馬”，but neither of these phrase is a subject。The second one is still on “她梳马/給她梳馬 ”, it’s too vague to just use these three or four words. There are many ways to just add one word or change some words to make it make sense, just like “她在梳馬”– She get her horse brushed. – could be a reply for “what is she doing”.
“她去梳馬”– She left for brushing her horse. – could be a reply for “where is she”.
拿梳子給她去梳馬的毛 – to bring brush to her so let her have her horse brushed.
The third one is “她” (在用梳子给) “她”，You see, character to character translation into Chinese would be : She use a brush to give herself – So, you
can see, it doesn’t make sense.
In Chinese “的”is used very often, same in English, You  your. for example, you are at a ranch and you want to have a ride, the rancher might say“here is your horse – 這是你的馬”.
Ok, I’m an English learner here in Taiwan. In this website, l have already learned a lot about English which I didn’t understand in the past.
I hope, my improvement-needed writing could help you a little bit in Chinese.