older dog with sudden bedtime behavior change

Hi, Everyone -- We've got a 12(ish)-year-old dog who we've had for three years now. She's always been excited to get into her bed (which we keep at the foot of our bed) when we were going to sleep and used to only be interested in getting in bed once every few months when there was a particularly bad storm, which we'd allow.

Early this week, however, her bedtime behavior changed. She'll still sometimes get into her bed, though on some nights she'll just stand at the bedroom door and stare at us while wagging her tail, as if asking for something. If she _does_ get into her bed, she'll only stay there for a few minutes before getting up and looking at us, wagging her tail, and crying. And invariably, she'll eventually try to jump in the bed, at which point we'll push her out. And she'll sometimes leave and go to another room in the apartment.

We're trying a bunch of ways to address this: getting her a really cozy new bed and putting some of our clothes in it (for their scent), giving her treats when she gets into bed and ignoring her when she begs to get into our bed, flipping around our own position in bed so that our heads are close to her bed (so she can feel closer to us while being in her bed), putting things alongside the bed to make it harder for her to get in, and of course pushing her out of bed when she manages to. But so far, nothing seems to be diminishing this nighttime drama.

Does anyone have any insights or suggestions to offer? I'm curious for any thoughts about what might be going on that would cause this to suddenly be an issue when it had never been one before. Is there anything connected with aging (she's no puppy!) that might explain this change of behavior?

Thanks!
Alan