Europe will be a lot of fun! Ein may feel like she's on her own 3-week vacation with a playmate.
I've never left Charlie, but several years ago I did take care of my dad's dog for seven weeks at my house while my mom was hospitalized. Rascal was very bonded to my father and the first two days she seemed sad and didn't eat much. By day 3, she started to enjoy herself, play, eat and act like her normal self. I do think dogs adjust to new situations as well or better than we humans do!
Have a great trip!