She's cute, but I don't like that she's only three and is likely bred. Minis generally have more foaling problems then other breeds so being so young and only 29" tall AND overweight...that would make me a little nervous.
She's way too small to be ridden, but she could be trained to pull a cart.
Also, keep in mind that you can find free horses all day long. Is she papered? Does she have any training? Is the foal able to be papered?
You'll also want to take into account the costs that go along with a horse if you haven't already. She'll need her hooves trimmed regularly so you'll need to find a farrier if you don't have one yet. She'll need her teeth floated as needed. You'll also need to purchase basic horse tack and supplies like a fly mask, hoof pick, brushes, halters, etc. A foal is also a lot of work and if it's a colt, you'll want to have him gelded. Foals need a lot of training and I wouldn't recommend them for a beginner.
I personally would pass on a trade and sell the goat to someone instead. Too many risks involved with this filly, in my opinion. And being that you could probably find one without the risks for free...it doesn't sound like that great of a deal to me. :shrug: