My dog is scared of our new rescue puppy… considering rehoming

I adopted a puppy (8 w/o pug mix) at an adoption event through our humane society. We wanted to try fostering the dog but the shelter said they do not allow fostering puppies because of the parvo risk. We also couldn’t set the dogs down to meet eachother because of the parvo risk but when we held their faces close together our chihuahua (2 y/o) seemed very curious and didn’t shy away from sniffing her, so we adopted the dog.

The puppy is such a good dog but our chihuahua doesn’t seem to be adapting well to her. Our chihuahua is very small (2 lbs) and still seems curious about the puppy from afar but anytime the puppy gets close to her she runs away. The puppy will sometimes run towards her or nip at her in an attempt to play but our chihuahua gets frightened and will run away or cower in a corner, getting tackled and nipped at while she waits for us to pick her up.

We’ve only had the puppy for 2 weeks but she’s already double the size of our chihuahua. The chihuahua’s separation anxiety has gotten worse and she shows less interest in playing or eating if my mom is not directly in the room.

I’ve been considering returning her to the humane society because she’s only 9-10 weeks old and will have the most success of finding/ adjusting to a new family but I’ve also gotten a lot of advice from friends telling me to try waiting it out because neither dog is showing direct aggression toward the other. My mom does not like the way our chihuahua has responded and is 100% for returning her but my dad doesn’t want to so the decision has been essentially left to me and I’m really at a loss. I just want what’s best for both dogs.