Well I think she's known for three things outside of Denmark: first her famous selfie, then her "Gucci" nickname and lastly her "Hi, I am the prime minister of Denmark". So in the current context where half of Europe wants to act more tough against Russia, her lightness was an important handicap compared to someone with a statesman image like Tusk. She suffered from the dumb blonde stereotype. 
Do you honestly think the choice of EU president will bother the Russians at all? I suspect they couldn't care less, and policy-wise it makes no difference for them at all (of course).
