PowerElite

So I'm re-reading the Mistborn series and this question popped into my head. I could have missed something, but I can't understand why Vin is able to absorb the mists. She's a Mistborn, yeah. A strong one too. That's rare but not unheard of. She's not even the strongest Mistborn either if we consider pure allomantic power. Elend and even Spook (at the end) are closer with their Allomancy than Vin is until she goes all 'God Mode'. So what was the deciding factor here? Did Preservation just close his eyes, point his finger, and it happened to land on Vin? Did Ruin? I know Ruin was driving Vins mother insane and all but then the question becomes: "Why Vins mother?" Could it have just been anyone as long as they were Mistborn?