I was wondering which tense should be used in the following sentences:

1. I inform someone that:

"I talked to my friend" or

"I have talked to my friend."

I think it's not important when I talked so I'd go for the second sentence.

2. When the person responds by saying: "When?", should I say:

"Today. She came to my house."

"Today. She has come to my house."

In this case I would go for the first one.

3. When the person wants to know the reason for the visit, should they say:

"She must have told you why she came."

"She must have told you why she has/had come."

In this case I'd say "why she came". Am I right?

Also, I wonder how native speakers would normally explain the above in an informal language. Could the verb "to come" be used if I wanted to explain that "My friend has come to my flat/to town/to the country" or should I use another verb/another phrase?

Thank you in advance,