I also have a .54 Renegade.
For a patched RB load I use 90 grains of 2f or 80 grains of 3f. These loads give me the best accuracy and I'd have no worries about shooting an elk out to 80 yards with this load. The RB is patched with .018" pillow ticking lightly lubed with Mink oil from Track of the Wolf.
I also have a conical load that shoots really well. Problem with it is it is Hornady 425 grain Great Plains Bullets, Hornady no longer makes them in .54 cal. This load I run 100 grains of 2f. It may shoot well with less powder, I haven't tested a lower charge. I started at 100 grains and it shot it so well that I just stayed with it.
The conical load has quite the recoil to it, quite a bit more than the round ball load. I think the common saying is "It kills at both ends".
If you want to run a conical you'll have to experiment a bit. These 1:48 twist TC's generally shoot a 1" or so long conical fairly well, personally I'd stick to something around 1" long. They will generally shoot a TC Maxi-ball type bullet well. If the bullet is a flat based design and not a hollow base, then a lightly greased 1/8" over powder wad will likely really help with accuracy.
I know less than nothing about the style of rifles that are forbidden to be discussed about here, so can't offer anything for your wife's rifle.
The sister forum to this site, ModernMuzzleloaders, will have plenty of folks that can help you out with that.