Continuity mistake: Selene normally wears high heel boots. They briefly turn into flats during her caged fight with Varga, right before he betrays her. (00:26:40)
Plot hole: This movie introduces, rather casually, nightshade as a vampire vulnerability. It works practically as in the videogame Skyrim, so whoever wrote it in the script most definitely played it. The problem of course is that a toxin that can murder most vampires and indefinitely paralyze the strongest elders, is a world-breaking concept that would have ended the war hundreds of years earlier, and instead is never used before or since the small scene it's instrumental to. Foreign translations which identify the nightshade with the more specific Belladonna plant (one of the most commonly used herbs since the ancient times) further aggravate the problem.
Continuity mistake: This film portrays vampires burning up instantly upon being touched by sunlight. Prior films showed the process as being less instantaneous, and potentially even survivable as long as they get out of the sunlight quickly enough.
Answer: Amelia was a Vampire Elder. She had responsibilities to the coven, to be gone for days or weeks would be normal, but months. Viktor had a suspicious nature. After discovering his daughter's affair with Lucian and the rebellion of the Lycans, he probably feared another betrayal.