Yeah, I believe it was the syphilis that was giving her the psychosis issues. I'm not a doctor, though.
There is also the element of what may have been subconscious influences on his film story lines, too.
I will agree that the idea of rescuing women is an element in several of his movies, but by varying degrees. Off the top of my head I can give you the following observations:
City Lights- This one is pretty cut and dry. We all know what happens here.
Modern Times- I see this as more of a mutualistic relationship between the two main protagonists rather than a "boy rescues girl" scenario.
The Circus- The Tramp "rescues" Merna from her abusive father, only at the end of the film he ultimately rejects her as being someone he can take care of, and marries her off the the tightrope walker.
The Immigrant- This one starts off with the Tramp saving the girl and her mother from poverty by protecting them from a thief. The Tramp had a love interest in the girl, but they both seemed to be in the same dire set of circumstances (both immigrants), so I'm not sure this qualifies as being rescued.
Sunnyside- The Tramp is worse off than the woman he is courting in this film.
The Gold Rush- The Tramp courts a woman better off than he is in this film as well, only to have the tables turned at the end of the film, when he becomes a millionaire, and plucks her out of poverty.
The Count- The Tramp attempts to court a rich woman while impersonating a count. (This one is a gem of a film, although the plot isn't very smooth, the gags are top notch).
Shoulder Arms- The Tramp runs into a french girl whom he rescues from some german soldiers. I don't remember how this one ends.
A Dog's Life- The Tramp rescues a woman from a dance hall for a happy ending.
The Vagabond- Charlie rescues a woman from a band of gypsies, and ends up being rescued by her when she is discovered to be a rich couple's lost daughter.
The Tramp- The Tramp has a love interest of the farmer's daughter in this one, but he ends up leaving after her fiance arrives.
The Face on the Bar Room Floor- This one is based off of the poem of the same name, so it doesn't really apply.
There are many more that I'm sure I'm missing. I think we should also take into account that Chaplin had to make films that made money, and at the time I'm sure boy meets girl in any varying degree always sold well. In addition, we should also take into consideration the evolution of the Tramp character. The Tramp of 1914 was not the same Tramp that we see in City Lights. Watching the earlier films and then moving into the later films you can sort of see the Tramp mature like a fine wine.