You are right that there is not humor in ch 32 and that here again Austen has used words like "miserable forever" and glow of gratitude. Yes, Austen is consistent in her description of Fanny's extremes of emotion.

I must disagree with you though when you compare miserable> gratitude> night sky. With such economy of words, I have to work out your meaning, and I assume you are saying that Fanny has irrationally transferred her misery and what should have been resentment towards her brutish uncle with fear of Mrs. Norris that boogeywoman who is the cause of all evil. Feel free to let me know if I have misunderstood.

Some of us previously said that we do think it is believable that Fanny could have extremes of emotion, where at one moment just one emotion can take over such as gratitude in this instance.

In about a quarter of an hour her uncle returned; she was almost ready to faint at the sight of him. He spoke calmly, however, without austerity, without reproach, and she revived a little. There was comfort, too, in his words, as well as his manner...

When she comes back to find a fire her gratitude rises again. “Heaven defend me from being ungrateful!”

Considering the tone of this whole thread, I think it bothers people that she doesn't resent Sir Thomas more, and maybe part of it is she doesn't have the highest self esteem. But also to look at it from a religious perspective, she turns the other cheek. It also seems some think that Sir Thomas' rant is evidence that he's been a brute to all of the children all along. I think Fanny's ability to revive shows she knows this was an out of the ordinary behavior from Sir Thomas. She also knows that his anger arose in part from not knowing the entire truth about Mr. Crawford which she has held back.

For more of Fanny's relief, when she goes to dinner she feels
Her uncle’s behaviour to her was then as nearly as possible what it had been before; she was sure he did not mean there should be any change, and that it was only her own conscience that could fancy any; but her aunt was soon quarrelling with her;

Just because her heart was filled with gratitude at one moment, doesn't mean that under the surface, she doesn't return to the misery she was feeling at Mr. Crawfords proposals which continue to be pressed upon her in the future depressing chapters. Nor does it mean she doesn't still feel misery for disappointing her uncle.- ch.37 she kissed the hand of her uncle with struggling sobs, because she had displeased him...

Lastly, she was all in a glow of gratitude that Sir Thomas did not give extra ammunition to Mrs. Norris, who had been a verbal abuser of Fanny since the age of 10. Imagine how that must have felt. A good day for Fanny is staying out Mrs. Norris' way. Judging by Mrs. Norris' quarreling at dinner it shows Fanny is right and rational!