Hi David
The suggestions you've made to your Nan are probably the best you can currently get, save for removing the bird feeders altogether, but it's likely Katie would just predate elsewhere, rather than stopping altogether. Even having a collar with a bell won't stop a determined cat, as they can learn to hunt stealthily enough to silence the bell. Shouting at a cat when they've brought you their kill doesn't help either. We've found the best way to deal with it is to remove the "gift" quietly and without fuss, and to offer a food treat - it may seem like you're rewarding "bad" behavior, but the cat sees only that they've honoured you with their friendship - handing over a meal is a big deal after all.
With regard to cats who're kept in for the first 6 months, in one word - Nah. Doesn't make any difference in my experience. Some cats like going out. Some cat love going out. Some cats love staying home. Often, the ones in the latter category, are cats who've been long time strays, typically entire toms subsequently neutered, who don't want to leave the comfort of a safe haven and regular meals. It does vary though from cat to cat.