I read this to mean that JA was drawing a comparison of the strength of Lady Russell's anger.

A kind of "like or as" or "indignant vs. ecstatic"

The inferior Mrs. Clay being held in such favor by Anne's relations, while Anne, who is clearly of dear and sparkling character, is dismissed and ignored and even chastized by her father and sister, [is as maddening in like degrees as] [it would be difficult for] a person who had been to Bath and enjoyed every possible cure, comfort and pleasure with new friends, and then must leave Bath and all of it's charms [has "mental space" to be mad]. "They are having too much fun to consider being mad about a single thing."

It seems an odd way to state the idea IMO, but that is how I understood the passage.