For those of you who may not know about the marchador--Marchadors are extremely slow to develop! It takes 6 years for them to be fully grown. So her body is extremely thin, but now she is starting to develop an neck and chest at the age of 3. They are gaited so the sickle hocks don't bother me. Please tell me if you see any defaults that standout.
I don't know anything about the breed so the things I'm listing may be normal for the breed
Fairly straight back, which might make the saddle slip around
And the neck is thin, but if she's still growing and filling out, it shouldn't be too much of a problem
First off I think she is gorgeous, and I applaud anyone who can keep a white horse clean!
I wont critique her head/throatlatch area as its mostly covered, so moving down to her neck, I think it needs more muscling, and needs to sit higher upon her chest but the muscling will probably come with more age. One of the characteristics of the breed is that its neck ties in smoothly, in one of your pictures it does, but inthe other it doesnt. Also I am not a fan of her shoulder angle as it is much to steep. Her back is short which I like. She appears to be calf kneed, and very sickle hocked which I don't believe is her breed standard.
But you appear to be doing a good job with her, and she looks pleasant to be around
Her pasterns seem upright. Her back looks pretty normal for the breed. What Sony is refering to that will prevent the saddle slipping is a crupper.
At the moment she has an upside down neck, but that can be fixed with work.
In the last foto she is toed out.