She does look like a sweetheart and for trail, personality is very important as long as her basic conformation is sound. I don't know if it's the angle of the picture but compared to her front end, her hind end is much smaller. She has a very deep heart girth/chest, shoulder angle isn't bad. Her neck is set pretty low on her shoulders, front legs are short with straight pasterns which will make her gaits more jarring, kind of hard to tell if her back is long or she just needs more weight across her loins, her head looks large in comparison to her neck and she looks like she's got low muscle tone. Is she an appy? If you vet check her and she's sound, you enjoy her, why not? I'm not so sure I'd be breeding her though. Plenty of horses with great conformation out there to be had for less money.
I don't know if it's so much that her legs are short, as her back is long. But regardless, she well be prone to early sway-back because of her weak loins. Her neck is attached low on her sholders and she is every-so-slightly sickle hocked with short, upright pasturns and a short croup.
Personally, I wouldn't breed her. May I ask why you want to breed her in the first place?
She's a cute mare, that's for sure - and she'll probably make a great trail mount, with trail horses I'd pick one with a great head (smarts) that can over look some small conformational "no-no's". I know first hand - I have a trail gelding who is very similar to your mare; long back, prone to weakness, and some small leg conformational defects. But, he's very smart and does his job extremely well, so he's my baby - as I'm sure she will be to you. :)
When I rode her her trot was pretty smooth compared to some trots I have riddin. It was pretty easy to sit. She went throught the woods great and played in the mud. Yes she is an appy. I'll find some other pics so there are diffrent angles.
Like everyone else said, she's very cute but absolutely not breeding quality. Her conformation looks sound enough to be a good trail horse and she'd look a lot better if she was fed and cleaned up. I'm sure she'd be great just for recreational riding.