In the book the fall of the usher what madeline thinking when she awakens to find herself in a casket?

Well, Madeline is pretty much a zombie at this point, so I don't really think she is thinking much once she wakes up from her death. She leaves her coffin and lunges towards her brother, who may be the one responsible for her death. Maybe she wanted revenge, which is why she took her brother with her to the realm of death.

From line 11 of ''Sympathy''   - 'When he fain would be on the bough a-swing' , I think the word 'bough' could mean something to rest on more like a stick or branch since the poem talks about a bird.

Explanation:  Reading from the beginning of the poem, we see that the poem talks about a bird. From line 10 before line 11 where the word 'bough' is mentioned:

''10. For he must fly back to his perch and cling''    

11. When he fain would be on the bough a-swing;

In my thoughts if a bird flies back to his perch and clings, perch is more like a resting place on a tree for birds and it clings, it is definitely holding on to something and since it's on the tree it would be majorly a branch on the tree. so this then gives an idea of what line 11 talks about. Furthermore, when an animal is a-swing like a bird or a monkey, it's from/on a branch usually strong enough to support it.

According to Merriam-webster dictionary, 'bough' means a branch of a tree, especially a main branch. It is pronounced /baʊ/