You've hit the nail on the head. She's displaying normal alpha female behaviour. The object is not to hurt the other dog, but only have it submissive to her. Now, that she does this at the park is kind of unusual unless she considers the park to be part of her territory. It sounds as though you go there often and see the same dogs, so she may have started accepting it as an extension of her territory and pack.
Now, then, what to do about it is a problem. I have seen an alpha in my pack "go after" a submissive dog in the park and, once the dominance thing is taken care of, they play happily together. But it still made me nervous and embarrassed at what humans perceive as bad manners. That's just it. To the dogs, what is happening is just part of their normal behaviour patterns. It takes training to make them understand that it is not acceptable behaviour.
Since you allow her to run freely at the dog park, there are a couple of options. When you catch her at this behaviour, say "No!" in a loud firm voice - enough to startle her - and then put her on her leash and make her stay on her leash for the rest of your stay. She will soon associate that behaviour with your displeasure and restriction in her play.
The second thing you could do is to buy a long leash (20') that will allow her to run a bit, but still give you control over her movements. It takes practice to learn to manage that much leash, but you'll get the hang of it. Then, when she takes off after a dog, you can stop her and say a firm "No!".
Of course, there is another trick but it's kind of "off the wall". When she runs one way, turn around and run the other way. Often, that will catch their attention and they will chase after you thinking you are leaving them.
my shep./husky is a bully - help! 
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