I think her health is not so great too. So I understand that. I guess when she wouldn't really answer what song she would sing, she already knew she couldn't make it. It was an all day funeral too, her schedule may not have permitted. She did read a little poem based on Twinkle, Twinkle Little Star she wrote for Whitney. That may have been the best she could do at the time.
I was surprised how many older stars were there and were okay to sit all that time! I'm thinking medication times, meals, bathroom breaks (that would have been me), moving around for circulation, you name it.
Let's face it: for anyone who has been entertaining as long as Franklin has, everything they say or do may be "show business". I'm speaking in general here, not accusing Franklin of being unusually dishonest.
But I am tempted to believe the claims of ill health. Singers the age of Franklin often do almost nothing except their shows and press appearances when they are performing; they simply have to conserve their energy. (I worked in the media department of a theater featuring senior performers. We had to be VERY careful with their time and energy.)
And as another poster pointed out, it was a long service. That would have been wearing for a 70-year-old singer with a show to do that night.
And the fact of the matter is, even if Franklin "didn't care" about Houston or her family (which I don't believe), it would have been in her best interest to appear at the service. Frankly, it would have been good p.r. for her tour.
So, yeah, I tend to believe Franklin was sick or just didn't have the stamina for the long service.