basically the 357 vaquero would have a similar feel with light 38sp, but has the option of heavier or faster loads as needed. The 45colt pushes harder and slow, the 357 is harder and quick, A 44mag can be loaded comfortably light, but most factory jacketed loadings are somewhat stout and can be somewhat intimidating to shoot for someone not used to big bore revolvers.
Muzzle energy gives some indication of what does what (range of factory loadings under saami max) handloads can go from next to nothing to probably a little above the max, cowboy loadings are near the bottom
32h&r 125-175
38sp 175-275
357mag 300-600
45colt 300-500
44sp 275-400
44mag 600-900
a 357 vaquero can give you a range from 175-600 with factory ammo, the vaquero is a little bigger and heavier than the single six, so the lighter 38sp loads will probably recoil less than what she is used to, and gives the most versatility, with less expensive components or ammo. 45colt is a handloaders cartridge, but is somewhat innacurate when loaded too lightly due to the large ammount of empty space in the cartridge, unless a filler is used, and factory ammo is expensive, and limited to mid-hot loads that are about equivalent to 45acp in feel
