That first question is really the core of it, isn't it.
So did the spirit whisper the truth to her? If not, how do you explain it?
Let me start by saying, and I'm sure we all know this, there are many people out there that are bad examples of what their church teaches. There are people that may or may not be trying to live up to what they are trying to represent. How many times have we stopped using a certain business franchise because we got bad service at one of them. That one employee had a uniform and a tag and represented the franchise, so we stopped buying from them. Was the bad service a good representation of the service you would have received from one of the owners, probably not. This is similar to what happens in religion, only times ten. The bad experiences that are tied to religion generally do not represent the teachings of that religion. Do LDS prophets and Apostles teach various leaders to guilt trip kids into "doing what they should"? No they don't. Sometimes Bishops and Stake Presidents don't handle things the best way, but most of the time they are trying. It is very difficult for someone who has had a, or many, bad experiences with a church to overcome those. This is just human nature I am talking about.
When I talk about the LDS church being the True Church I am not talking about the people in it being perfect. I am not talking about the leaders in it being perfect. I am talking about the Church having the real Authority from Christ to do some things in his name. Does that mean the Prophet walks around all day every day, and everything he says or does is straight from Christ? No, I don't think so.
What's my point? I thought those ideas were important to the discussion. There are many very good Christians in the LDS church. There are many very good Christians in other religions. The LDS church certainly does not as someone mentioned earlier, corner the market on being Christians, living good lives, giving to others, having charity, or anything like that. They also have their fair share of people that are having a hard time living those principles. They also have enough "wolves in sheep's clothing" running around hurting people in the name of good.
What I believe the LDS Church has that other churches do not have is the Authority to perform ordinances in the name of Christ that truly will last after death. Does that mean that LDS members are better than anyone else? Nope. Does that mean we are more charitable than anyone else? Nope. Does that mean we are immune from hurting other people, or saying and doing stupid things? Nope.
I guess my idea of the Truth's that need to be proven for each individual, somewhat in this order are: (maybe not in this order, I am just throwing them up there)
Does God exist?
Is Christ the Son of God?
Did he truly Atone for our sins?
Is the Bible the word of God?
Is the Book of Mormon the word of God?
Does God still speak through Prophets?
Was Joseph Smith a Prophet?
Is the current LDS Prophet a Prophet?
Is the Priesthood authority truly the authority to perform ordinances in the name of Christ?
Is the Church of Jesus Christ of Latter Day Saints truly the Church of Christ today?
(I'm sure I misses something, but do the same thing with every question after this)
How to answer these questions is specific to you, but some of the ways are to think it through and see if it truly makes sense. Study it out and see if you understand it fully. Live your life like the question is true and see if it makes a difference in your life. Ask God to answer your question. I'm sure I missed some other ideas that help people get the answers they are looking for.
I think my point here is that you can't just jump to the last question on your list, it's like building a cathedral or temple, you have to start answering the foundation questions before you can get to some of the more in depth or convoluted questions.
I think I am done rambling and answering nothing. These questions are hard for me because I feel like the question to fully be answered it would have to take a year of constant discussion and action.