Just to interject, the BLR is the stronger action (lever actuated bolt action) as it is capable of handling the 300 WSM which has operating pressures in around 63000 CUP - max for the Marlin 1895 action is around 43-44,000 CUP with the 444 Marlin and 450 Marlin. You don't see the Marlin 1895 action being rechambered for the 300 WSM or similar high pressure cartridges from the factory or by gunsmiths.
However, there is something to be said for slinging 405 grain hard cast or premium jacketed bullets at a charging bear versus 200 or 250 grain bullets in the .358 Winchester. More penetration and bigger hole with the .458 cal sized bullet then the .358 cal sized bullet. I believe this is what 303carbine was getting at.
That said, the 450 Marlin or better still, the .45-70 Govt would be my cartridge of choice - if you do go this route, be sure to get a good quality recoil pad installed on the gun that will tame the heavier factory loads such as PMC 350 grain jacketed flat point +P+ loads. If you reload, you can make your own heavy bear loads from either hardcast lead bullets or premium jacketed bullets such as Nosler's Partition or Swift's 400 grain bonded bullet. You may also want to put on a good quality ghost ring sight such as that from XS Sight systems or Wild West Guns or other manufacturers for aiming quickly at targets. The tubular magazine Marlin has is pretty reliable in my experience - and depending which version you get - Cowboy can pack up to 9 cartridges with the chamber empty or 4 with the guide gun and regular 22 inch 1895(empty chamber as well). The BLR in .358 Winchester will have only 4 rounds in the detachable magazine(empty chamber) and 3 in the .450 Marlin chambering(again, empty chamber). You would be better off with more rounds available as in the Marlin 1895.
Whichever way you go, both you and your wife should practice regularly with the new rifle to be able to confidently use it in critical situations without delay and be able to aim accurately under pressure. The lever action Marlin 1895 gets pretty smooth with practice.
For the record I have 3 Marlin 1895 leverguns - Guide Gun, regular 22 incher and Cowboy Action in .45-70 Govt., enjoy all three, and would have no problems using any of these on a charging bear if the situation arose. Also have a 336C in .35 Remington, but would hesitate using this on Grizzlies unless I had no choice.
Consider checking out the various levergun forums - leverguns.com, marlinowners.com, shootersforum.com, 24 hour campfire, etc. for more information