I switched Indy at 7 months. He is happy and healthy and it went really well. The first few feedings, he looked at me like I gave him the wrong dinner and then just gobbled it up. We didn't do a drastic change. We started with Blue Buffalo Large Breed Puppy and just graduated to the same flavor in Adult. I think you should be fine to switch Boo when you run out of what you are giving her now.
My vet says a year also.
My vet recommends all puppies be switched to adult food at 14-18 wks! I fed Wellness Super5 Puppy, have now switched to Wellness Super5 Adult. Some folks say you never really need puppy food, just premium quality all-life-stages or adult food.
The reason the large breed puppy food is recommended is it has lower calcium and some other supplements than regular puppy food. Some puppy foods, especially the premium brands, have too much protein which makes puppies grow too fast. Corgis are a dwarf breed, but the way their bones develop is similar to large breeds, apparently. Slower growth is better.
I wouldn't worry too much about having done damage...just keep her physically fit, feed good quality food, don't let her get fat, she should be fine.
If she's doing well on whatever you're feeding her, and it's a high quality food, just switch to the regular adult version of that food. It can get really confusing comparing different brands, nutrient profiles, ingredients, etc.
i just switched linus at 1 year. the vet kept him on the puppy food because vitamin supplements seemed to not agree with him and bb has "life source bits" that i guess had more vitamins. he's getting the same kind of adult food and seems ok with it. the vet said he looks "lean" for a corgi, but i think he's really just not an overweight corgi, which may be what she's more used to seeing.
You can switch to a regular adult food now. Many people recommend using an ALS or large breed puppy formula to keep them from growing too quickly when they're young. I would not use a large breed adult food though.