I also imagine it was a regular thing to have her over for dinner since they lived so close to one another. I’m sure they had developed a routine of them pulling up and her going in through the door because it was a common occurrence. I truly don’t see anything odd about this.I agree with you but I'm slightly perturbed that you made this post in response to someone pointing out that all older people are different and that some older people are mobile and independent, when the majority of comments using their own experience as proxies are coming from the "anyone who leaves an older person alone is dodgy" crowd, who are not only infantalising a woman on no grounds at all, but badmouthing the non-suspect relatives of a missing and potentially murdered woman who are no doubt going through hell.
There's absolutely nothing weird or odd about only taking three minutes to say goodbye and walk someone into their house at night, rather than coming inside with them and spending time "getting them settled" whatever that means. People only think it's weird because they're looking at it in the context of an elderly kidnapped woman. In real life it's a completely normal thing no one would even blink twice at. Most people are tired after hours of socialising outside of their own home and just want to be alone in their own space, older people get more easily tired. I don't know a single elderly person who would want someone coming inside their house to spend ages fussing over them at the end of a long, tiring day, rather than simply doing a completely normal standard goodbye.
Bottom line, they know their mother, and we do not. They know if she's the kind of person who wants people to come inside her house and spend time getting her settled when they drop her off at night, or the kind of person who is happy to do a normal regular goodbye.