Translation:She would have gotten a really cool birthday present, if she had been nice.
The pronunciation of "fødselsdagsgave" should be updated to match how this is really said in Danish.
sej = tough, ductile, viscous, impressive, cool
fed = fat(ty), chubby, obese, rich (about food), bold (about font), cool
cool = cool
Sejere is the comparative form, meaning "cooler". But getting a "really cooler" present doesn't work too well. :´)
You are right. It should be an option. Maybe not the most natural thing to say, though.