Two separate events happening to Susan on that morning is at least one too many for me. A small town...two different criminals appearing early in the morning to rob, or abduct this woman? I can't buy that, JMO.
I'm thinking about the wallet as being more along the lines of a quick/easy grab. I agree that two people showing up with the intent to confront/rob/abduct her would be really unlikely though. If the money/cards were removed from the wallet separately I think it was more like someone walking by and saying "oh hey look, a wallet, wonder if there's cash in it?"
Not necessarily related to the two separate incident theory, I'm just wondering, where are you getting "small town" from? I know it's all relative to other places you've been, lived, etc. and maybe it's just me, but I don't think of Roseville as small. It's a pretty busy suburb of Sacramento. Population wise, according to this site: http://www.city-data.com/city/Roseville-California.html the population was about 119,000 in 2011. It's not LA or New York or anything, but at least in my experience that's a fairly decent sized city. Actually I was surprised to see that Roseville's population is more than double where I live, another suburb of Sacramento that I also wouldn't consider small.
More than you ever wanted to know about California city populations: http://www.city-data.com/city/California.html, Roseville: https://en.wikipedia.org/wiki/Roseville,_Ca, and population sizes in general: List of United States cities by population - Wikipedia, the free encyclopedia (Roseville is listed as 211th largest in the US at about 124,000 people - not sure what census data they're using here). I wouldn't consider it a big booming metropolis or anything, but IMO it's not really small.
I don't know if it matters or how this relates to finding Susan.

ETA: sorry the US Cities list quote is coming up so weird and duplicating. I've tried to fix it but can't figure out what's wrong/why it's doing that. It goes to the right page, just looks funky here.