Honestly, I wouldn't go for a Bernese right away if she's looking for a dog park dog. They're certainly far from DA or even animal aggressive in the way lots of other breeds are, but the ones around here are quite protective. I definitely wouldn't say aggressive, but they're wary of visitors in the home, and won't hesitant to nip a stranger who grabs at them.
I'm not sure if that's the standard, or very common with good breeders, but it seems to be the case for the dozen Berners I've met in this area.
I would recommend a Newfie or St. Bernard before I recommended a Berner. She could probably find a Great Dane breeder that breeds to what she wants, too.
Rotties and Great Pyranees are also definitely not dog park dogs, or "love-everybody" dogs - although I have met quite a few "watered dog" adult rescue rotties who fit that bill, if she was interested in going that route.