Advise Please.

Glad your puppy is okay. I agree with everyone to not trust the owner about "my dog is great". They probably are, maybe the dog hasn't been socialized much with puppies..
I read the local news a long time ago that a family has a adult male german shepherd dog (i forgot the age of the dog) that they claim good with people. One day the maid bring her 1.5 yo baby to work because she couldn't find a sitter. When she was doing laundry, she put her child nearby on the floor and didn't realize the dog was approaching. She suddenly heard her child scream and the dog was literally dragging her by the head. She screamed hysterically and the owner's son was home. He couldn't get the dog to release the head in time and the child was rushed off to the hospital. She eventually died from her injuries. The family claimed it is a first time the dog is aggressive and it's like the dog is possessed or something, and decided to put the dog to sleep after the incident.
Just because a dog was never aggressive doesn't mean they won't, especially the kind of dogs that known to be aggressive (pit bull, etc)

Hope she's ok, poor baby!

I always keep an eye on dogs at the dog park who 'charge'. It's one thing if they see another dog and trot over, but another thing if they're racing up (goldens are guilty of this a lot...). Also another thing if it's more than one dog, that's a pack, and if it's a breed that usually isn't good with other dogs or can be an issue with other dogs (like terriers). I'm sure there's exceptions to the rules, but I don't like to assume.

Not all dogs who go to the dog park are great with other dogs, and not all owners have brains. I remember one time someone brought a very young, very small puppy to the park, it was screaming when other dogs got too close. We were up on the hill and could see a big area. It was a bit creepy how when that dog screamed, 5-7 dogs from different areas all noticed and started to head in that direction with their hackles up... most would come back after the owners called them or the screaming stopped, but still...

What you can do is step in front of the approaching dogs and stomp/growl at them. If nothing else this often will make them stop and think twice about flying into the situation (you become your pup's defender of sorts, or at least redirect their attention a bit). It also teaches your pup that you are there to help in those situations. Carry a spray bottle of water if you want to shoot dogs who come too close as well (if it's a huge issue).

With your pup, find some little dogs who are good with puppies and make sure she has some positive experiences with little dogs to balance things out so she doesn't think all little dogs are like that. My old border collie got attacked a few times by a GSD, and so started to worry about them when one was near. Found a friend with a GSD who was just going into season and very flirty, let them party for a few minutes and he decided that not all GSD's were so bad to be around....

Lana

As someone mentioned, if sometimes helps just to step in front of your dog, or call out a command to the dogs approaching. It gives them a moment to pause and gives you a moment to assess the situation. As I was walking Logan and Lacey, our Golden's, and Ralphie the Corgi the other evening. We passed a house where we know the little "Toto-type" dog who lives there. He happened to be on leash as the owner was getting ready for a walk. Buster started barking and taking a very defensive stand. No threat to us as he was on a leash. As the owner walked out to the street, you could tell Buster was a bit distrustful of us, even though he has seen us before. The owner said he had been jumped at the dog park, so now Buster was taking the defensive position first. I had the Goldens sit, and let Ralphie (since he was more his size) walk up to him, sniff noses, wag tails and we then left on a positive note for Buster. As we were returning we saw Buster on his return trip. Again, we did the same thing. The owner thanked me for taking the time to do this with Buster. Hopefully we did a little bit to help Buster realize not all dogs are as mean as the one at the dog park.

If you have your pup on the lead, and loose dogs approach, it can be very stressful for you and the pup, but you must try to keep a cool head if possible, as your pup could view any other dog approaching as something to fear. Instead as others have said, straighten up, shoulders back, and put yourself between the other dog and your pup. I like the idea of the water bottle also. If the other dogs are "fixated", a quick squirt or "oi!" shouted from you could be enough to stop their intent.

I find now that if a dog is being aggressive, Obi (who interacts more than Izzie) will run behind me. I guess if a dog does that, I have to act as a leader and protect him, right? He's a big boy too!! I would much rather he did that than engaged in agressive behaviour!

I don't know what it is about some dogs just going for pups, heck Lexi (5 months now) has been bitten several times, by Collies mostly, when she's been on the lead!! Luckily, she has lots of experience with many other dogs of all shapes and sizes and it hasn't put her back.

It's so important your pup learns how to behave around all types of dog, it's how they learn about body language, posturing, etc, and should help her as an adult to interpret other dogs' intent, and also help her to act appropriately.

Is there another place you could walk? If there were agressive dogs at the dog park, I would definitely not be taking my pup in there.