In English, we can comfortably shorten Elizabeth to Elsie. And in both German and Dutch, a diminutive can be formed with -chen, -ken or -ke (as well as other spellings that make a k sound). That is where Elske comes from ... same Els- as Elsie, and then the -ke ... though luckily for your friend it's also a comfortable merger of two family names. Not all mergers are successful!