45 caliber bullets for center fire cartridges will not work well. The size is wrong. A 45 cal ML will have about a .450 bore. The groves will be about 0.012". That gives a groove to groove diameter of about 0.0474".
Your lead 45 cal pistol (0.452") or a rifle bullet (0.459") will be larger than the bore and less than the groove. IT will be hard to load due to the alloy and leak gas in the grooves when fired.
For a club shooting target rifle I like the 40 very much. It is large enough to be easy to manage. Light rifles are around. The amount of lead an powder is less that the 45. Going smaller to the 36 or 32, especially the 32, loading becomes fiddley.
If she wants to hunt big game, get a big bore rifle, IMHO....