Looking for a good rifle for my rather petite GF/soon-to-be-wife. ...I'm thinking .45 caliber.
Are you worried about weight of the rifle, or recoil, or strength to hold it when shouldered? Some of all three or all of all three?
While the Cherokee and the Seneca are great rifles in .45..., the problem you have is that they cost pretty much what some of the new rifles cost, and since they are out of production..., replacement parts may be troublesome.
Recoil, first will be helped a lot by using round ball and not conical. Next..., it will be based on the powder charge. Next, how well the stock fits her and how is the butt plate constructed. (The Seneca and Cherokee both have brass butt plates.) Finally the mass of the rifle will help a small amount to absorb recoil.
The length of the rifle may or may not be a factor for her. Shorter rifles are often easier to manage in thick brush, BUT a very short barrel means a short sight plane, and perhaps a heavier charge to get optimal performance on game. On the other hand the longer that barrel, usually means the more leverage gravity exerts on the shooter to hold the rifle up when sighting.
Number one choice seems like the Lyman Deer Stalker in .50. They come with a rubber recoil pad and fiber optic sights.
Number two choice seems like a Pedersoli Frontier, perhaps in .45 (if it can be found). A .50 will work. Has a metal butt plate, but..., it has a 14" longer barrel, which will give a much longer sight plane and make it easier for the shooter to be accurate.
LD