Puppy socialization window is short!!! IMO, puppy comes first... if you can only bring one dog, bring Didgie, because socialization is important for the rest of her life. Did you feel guilty bringing Trav out to socialize him and leaving Kaylee at home? I think you're just used to babying Trav and doing everything with him, but part of having 2 dogs is establishing priorities. Socializing the puppy is #1!
That said, do your best to make it up to Trav with one-on-one time and training, while realizing that it won't always be like this! One day (sooner than you can even imagine), Didgie will be a grown adult Koolie, she'll be well trained and well socialized and you can bring both of them everywhere and split up one-dog outings evenly.
I didn't feel too guilty about Gonzo, when I got Fozzie. Gonzo was thrilled to have a little brother so I think that made up for it! I would bring Fozzie to events, fairs, pet stores, friend/family houses, etc alone... so that I could focus on giving him positive experiences with people and other animals. I would take Gonzo to the park or lake almost every day, sometimes with Fozzie and sometimes without, to keep him happy. I would take Fozzie along with me and Gonzo to flyball and agility practice, dog playdates, etc and bring crates so that I could spend individual time with each of them and also time together. When ever I left Gonzo, I'd give him amazing chewies, stuffed kongs, raw bones, and he actually started looking forward to me and Fozzie leaving! In the end, Trav did get your undivided attention when he was a puppy, and Didgie deserves lots of training and attention too. Not only for socializing and training, but to cement your bond with her. You and Trav are already bonded, he's very well trained, and you don't need to feel guilty if you have to put working with him on the backburner to work with Didgie during her foundation of life. I'm sure Trav won't mind as long as he gets plenty of swimming and ball time. ^.^