Because she has a job on this earth
That is to spread christ's word
If I kill her, I might as well condemn those ,the ones she is here to reach or at least plant the seeds of Christ in, to hell
Or, in other words, you care more about the possible salvation of some than the guaranteed salvation of a loved one (well, technically it's more the possible salvation of some vs the guaranteed salvation of an individual, but if the original framing is more emotionally charged, we can roll with that), and you're willing to allow that loved one to risk eternal damnation in order to possibly enable them to save those other few.
That's a pretty tricky one, from a morality standpoint. Guaranteed infinite reward is pretty close to impossible to top, and willfully choosing to deny someone that is something very hard to justify. It's also really hard to balance allowing a potential for infinite punishment by not doing so. It would definitely seem that, from your perspective, the best thing you can do
for your family member would be to kill them (ruddy strange though that is). This would actually be true for
any individual in similar circumstances -- no matter how many people they
may bring to salvation, it's almost certainly not worth the risk involved.
Of course, you can also just say that, yes, you value the salvation of others over the salvation of your loved one, or that you believe that choice is more important than heaven, among other things. It almost certainly means you're not doing the best you could for the individual being considered for early ascension. There's not much on earth that
can top an immediate get-into-heaven card. It's basically impossible to top infinite consequence in a finite time frame -- that's one of the basic premises behind a lot of christian evangelicalism, even, that infinite reward and/or punishment trumps finite concerns.
No
You have the choice to do your job
Killing them would also take away their choice
I don't think a little thing like finite agency could make up the difference of the potential for absolute and infinite torture, especially in the face of guaranteed infinite reward. There's not really anything
can do in the finite realm that tilts those odds in the favor of the potential for infinite punishment. It's one of those nasty metaphysical consequences that tend to pop up when discussing things like that.