Let me see if I can clarify this for you. Both sentences could be correct in certain situations.
1. This is a speculation on the part of the speaker. He (or she) is guessing what would happen if Kate tried to come here. Perhaps our house is difficult to find or perhaps Kate doesn't know our city very well. But the speaker is certain that Kate wouldn't lose her way if she decided to come to visit us because she's been here before.
2. I think the second sentence is a response to someone having said, "I think Kate has lost her way." But the speaker doesn't agree because Kate has come here before so she should know the way.
I hope this helps. If you are still not clear on it, feel free to send me a private message and we can discuss it further.