I found it somewhat ironic that my thread here only got one or two replies
(And if that isn't irony, I give up! It seems so hard to define!)
The same thing happened the other day, she talked all about her day and when it was my turn she suddenly turned off and got distracted by everything, didn't ask any questions or respond at all. When I just stopped mid-sentence and gave her another change to talk about whatever she wanted she asked why I stopped talking. I told her I could see she wasn't really interested and again she claimed she was, but her actions and her words didn't quite match up.
Ah well, I've always kept lots to myself and let other people talk ahd share their stuff with me, so I think I'll just keep doing that. I'ts what I've always done anyway.
If she asks in future I'll start, but if I can see her attention waning then I'll just let her talk instead.