When I'm traveling (10 hrs) home to see my mom I'm usually eager to get there so I fill up with gas before heading out and I don't stop again until I'm down to a quarter of a tank. Depending on the mileage her car gets per tank I would use that as a gauge to when and where she might have stopped for gas, for me it's usually 6 hours down the road but I drive an 1/2 ton Dodge truck with a hemi...she was driving a smaller type car so she could have certainly driven for more than 6 hours on a tank of gas.
If I'm making a longer trip such as 16 hours, 10 hours is my max driving time, period. I just can't function on the highway after 10 hours, so I usually set that as my pullover and get a hotel time limit.
Depending on how much she loves to sleep would probably be a good gauge to estimate what time she would have left a roadside hotel and headed on to San Antonio, that along with the time of her arrival and check in at the hotel should give a pretty good estimate of where she may have spent the night. So is she an early riser or a late sleeper? Logan lived with her for 2 years so he should be able to estimate about what time she would have gotten up.
Do we have an approximate time as to when she met Tammi at the church to get Gabriel?