The western black-legged tick is the vector for Lyme disease West of the Rockies, and it is very small, even when engorged.
Quick and correct tick removal dramatically lowers the chances of transmission of tick-borne illness, so it's pretty unlikely that Molly will get any disease at all. Transmission rates are low to begin with, and lower still when the tick is removed within 24 hours.
For more info on black-legged ticks, take a look at this page: http://www.phac-aspc.gc.ca/id-mi/tickinfo-eng.php
. It's a Canadian public health site, and it has photos of black-legged ticks (in various life stages and stages of engorgement) that may be helpful in determining whether or not Molly's tick was a black-legged tick.
It's still a good idea to keep a close eye on her and have her tested for Lyme and other tick-borne illnesses in a few months, but I would say that it's unlikely that the tick was a black-legged tick, and also unlikely that the tick had time to transmit any infections to her in the extremely short time it was attached to her.