Feedback on slight behavior changes

First, I'm a big fan of the feedback model and while I have much more room for improvement I am making progress. The issue I'm having currently is with one of my top performing managers. I'm noticing some slight changes in her behavior but it's somewhat hard to describe so I don't quite feel right giving feedback because I don't think I can describe to her what I'm seeing. It's kind of like her head isn't 'in the game' as it usually is. I'll try to describe a few things here:
1) Responsiveness isn't as normal but not non-responsive just less than usual. When I delegate or ask for something it takes longer or I have to remind more than normal
2) Deadlines are starting to slip slightly. Not on anything mission critical nevertheless on tasks that are part of our department goals/objectives for the year.
3) Follow up isn't as frequent on standard processes that require it. For example following up on monthly reports which indicate action is required by other work groups.
4) Work hours seem to be getting shorter. This is a tricky one as I am a strong believer in being flexible with work hours for professional managers but I do expect to be able to communicate with them as needed during reasonable work hours. This person typically comes in a little later than most and stays a little later which is fine. It's hard to say for sure but arival seems to be getting later and leaving seems to be getting earlier as well as longer lunches (I don't track time and am not about to start). The other day an urgent customer issue came up at around 7am. I called the manager's cell phone and left a message to call me back asap (note that it is very rare that I call early). They didn't return my call and didn't get to the office until close to 9am (business hours are typically 8-5 but many start earlier as our customer is 2-3 hours ahead of us). Acknowledgement of my message never was done the entire day.
5) Tone in our interactions seems to be more irritable lately. For example in preparing for a presentation, the manager 'snapped' at me as I was editing their slides.
6) Her overall mood and attitude, while not bad, just don't seem to be nearly as positive as normal.

Basically it's several little things that are adding up while the big things like customer service and meeting critical deadlines with high quality work are still there.

What do I do? Wait and focus more on documenting and describing specific behaviors? Observe and wait to see if performance starts to slip in more significant areas? I don't want to seem like I'm picking on all the small stuff.