This is extremely similar to my own cat and dog.
I have a small dog that loves to chase birds and she used to chase my cat as well. So for the first several months we had to keep a very watchful eye on her and reprimand her for cat chasing. But we also created several high perches and walkways for the cat so she could move around without being chased. We did notice that the chasing almost always happened outside because there was more free space for running. In the house the cat had more hiding spaces and less incentive to run off.
Now we're at the stage that the dog wants to play with the cat, but the cat doesn't want to reciprocate. We let them interact freely, but when we notice that the cat wants to get away from the insistant dog, we divide them again.
My advice for you is to let both pets meet in a calm environment. That includes going on a walk with the dog before introductions, so the dog has already burned off excess energy and isn't too wild. Make sure your cat has several hiding spots where the dog cannot follow, like under the bed, behind or on top of some furniture or on a window sil.
Both pets have to learn to interact and communicate with each other. Our own dog was also too insistent with constantly sniffing and gradually the cat learned to swat her away if it's too much. In turn the dog is now learning how much sniffing is too much. That is a process that takes time. You can compare the brain of a dog with that of an (approximately) 5 - 6 years old child that wants to play with a cat. Learning restraint and regulating their excitement is hard and takes time.
You can help regulate your dog by sitting between both pets. Let them interact, but when you think the dog is too pushy, push her back away from the cat.
As for the pouncing: it's very unlikely that the dog would attack the cat after they alredy got to know each other and interacted several times. Maybe your dog is play bowing? Here is one example video that explains the play bow. It's primarily an invitation to play in dog body language.
Although the person in the video correctly mentions that dogs can do play bows in a conflict situation, the gesture is always meant to deescalate and resolve the conflict.