I think pictures would be helpful.
I'm not a huge believer in the whole "sweat pattern" thing as a "the saddle fits or it doesn't" diagnostic. I've seen plenty of horses that just sweat tons under the saddle, making the saddle fit look "good" sweat-wise when that same saddle obviously fits badly upon visual inspection.
I think it has it's place when the saddle appears to fit well, to help you cement the idea that the saddle does really fit well, or to make you question if the saddle fits as well as you think, but not as a first step in saddle fitting. :)
Anyway, to me it sounds like you might need a better fitting saddle. Good news, you can probably find a used replacement for rather cheaply without needing to sell this saddle since you said it has sentimental value.
I found a BigHorn synthetic western saddle (one of the most quality synthetic western saddles out there) online for $75, it just needed a little cleaning up that I could do which, once done, that saddle looks like a million bucks (for a synthetic).
Depending on your needs you can probably find a suitable saddle for your girl without breaking the bank/selling the other saddle. :)
Anyway, pictures would be beneficial.
Fabio - 13 year old Arabian/Lipizzan gelding
Rest peacefully, Lacey.