Behavior from my dog when introducing a cat

My dog (almost 5 y/o golden retriever) has never shown any aggression to animals or people. My husband was on his lunch break at work when he saw a car pull up and dump a cat in the parking lot. If the two get along we are interested in keeping the cat. Don’t fret – I have a vet appointment set up to have the cat checked out and to see if there is a microchip present. My dog has been around cats before. Her first encounter was when she was a puppy going to obedience training an the trainer had a cat there who was very confident and comfortable around dogs. My dog did well with this cat (sniffing, licking, play bowing). When my husband brought this cat home we placed him in one of our bathrooms where he has his food, water, litter box, and a bed. We have allowed the to sniff each other through a closed door and that seems to have gone well. The first day my dog would stand/lay outside the bathroom and seemed very interested about what might be in there. The next day she showed some interest in the door but quickly moved on and did not lay outside the door. We have allowed the cat to come out and explore and to sniff around.

We let them meet face to face for the first time tonight by placing our dog in her crate (that she is very fond of and comfortable in) and allowed the cat to free roam in the room where the crate is. The cat, from what I can tell, did well (no fluffy tail, no hissing/growling, purring, flopping over and rubbing on the floor and us). The cat did approach the crate a couple times to sniff but other than that seemed disinterested in our dog. My dog was sitting in her crate and appeared relaxed at the beginning (relaxed ears, no panting) but she was staring at the cat. She would occasionally paw at the crate door. We did this for about 5 minutes when our dog started to pant lightly and was frequently licking her lips. I will say if the cat moved quickly, our dog when also make a quick motion toward the crate door.

What are your opinions? Is this behavior from our dog normal? Is it prey-drive? Again, she has never once shown any form of aggression towards anyone or anything.. but I know that doesn’t necessarily mean they will get along.