This is a 2003 study, but I've read this general pattern still holds true. If so, it suggests in 76% of known cases, people are kidnapped by someone they know (family or acquaintance) and in 24%, it's random/stranger.
This (in addition to no signs of struggle, as of yet) leads me to lean toward known acquaintance.
"Based on the identity of the perpetrator, there are three distinct types of kidnapping: kidnapping by a relative of the victim or "family kidnapping" (49 percent); kidnapping by an acquaintance of the victim or "acquaintance kidnapping" (27 percent); and kidnapping by a stranger to the victim or "stranger kidnapping" (24 percent)."
Thursday Edition: Kidnapping Facts
I checked, and as I suspected, the vast majority of family kidnappings were parents stealing their own young children--custody cases and such. I wouldn't be surprised if almost all the rest of family kidnappings were estranged husbands kidnapping their wives.
So, going by the stats, we'd have a slightly more than 50% chance of her being abducted by an acquaintance, and slightly less than 50% chance of it being a stranger.