I actually can speak from experience recently with the very same problem. I have an 11 year old rottie who has lost her other canine companions one by one over the bast 2 years from old age. She is set in her ways and we knew bringing a puppy home would cause friction. We have had the puppy in the house for 6 weeks so far. At first we would just separate them completely because I did not feel safe with my rottie close to the pup at all cuz it takes a second for a tragic accident to happen.
I would say after 2 weeks or so of my rottie getting used to the scent of a new puppy in the house and hearing her barks, whines...etc. She was now familiar with the pup on some level.
We gradually introduced the pup to the rottie and definately met resistance over and over again. The rottie's hair would stand all up like a mohawk and she'd growl and retreat to another room to get away from her. This went on for another week or two of the same thing day after day.
Then we would put the puppy down on the floor and be ready to grab if the rottie made any attempt to bite her. So far... the rottie has accepted the fact that there is a new pup in the house. She is still moody about it and definately continues to growl at her and even nipped her once to show her who was boss... but she's never tried to hurt her. I've even caught her playing with her a few times. Just the other night my hubby was playing with the pup on our bedroom floor and the cat decided to ambush the puppy and smacked her with his paw really hard. When he wound up to bat her again with his other paw the rottie jumped up and ran over and scared the cat away from the puppy.. it was the sweatest thing ever...lol But I would never trust them alone together because any dog can be unpredictable.
It took some patience and time... but they are SLOWLY becoming companions. I look forward to the day the rottie will let the puppy cuddle with her. At least I hope it gets to that point. If not... I can accept the way it is now.. we can all reside under one roof with no major malfunctions aside from potty training hell.
Goodluck with getting your corgi to accept the puppy... it just might take a little while for her to realize you have an addition and that it doesn't mean she's on the back burner. Just remember to give your corgi just as much attention you give to the pup because dogs do get jealous just like people do. Make her feel special so the puppy is not a threat to her.
