How has the relationship between Rochester and Jane changed by the time he proposes a second time?
When Rochester first proposes to Jane Eyre there are two major obstacles, from Jane's point of view, to the proposal. The first is that Rochester is married. His wife Bertha, although insane, is actually alive and living in the attic of his house under the care of Grace Poole. Bigamy is not only illegal, but also goes against the Bible, and Jane, had she accepted the offer, would have technically been living in sin. She also is uncomfortable with the inequality of the relationship, in which she would bring nothing (she is a poor orphan) and he would bring everything (as a rich man).
The situation of the second proposal is radically different. Bertha is dead, and so Rochester can marry Jane legally and legitimately. Jane has inherited money, and they are economic equals. Rochester has been blinded and crippled, resulting in equality of power in the relationship.