ANY horse can do trails to some capacity. I'll address the stock work.
I think she has the look of a horse that can get down and turn quick, accelerate fast, and stop fast. In other words, physically, she has the look of a horse that would make a GREAT cow horse. Question is, how cowy is she? THAT will dictate how well she does working cattle.
As an aside, my level-to-uphill, long-backed anglo arab is a pretty handy "cow" horse, and he's definitely NOT built for it! I tried "cutting" a horse with him and once he figured out what I wanted him to do I barely had to touch him. I know another anglo arab that's built similar, just with a shorter back, and she's a top campdrafter (do you have campdrafting in the US?) having won state champ A grade horse in her youth. It's more about the cow sense than the confo.
All that being said, I really like your girl. I have a weakness for chestnut overos, especially splash/sabino/frame combination overos like her... I wouldn't buy her myself, because I ride jumpers and she's not built for it, but she looks like she'll be a fun ride and she should do what you want her to do.
A CLEAN SLATE FOR THE FUTURE