Is there a typo ?

If a noun starts with a vowel, the preceding possessive pronoun always takes the masculine form. This is to avoid the clash of two vowels, as in ma amie.

mon ami -- my (male) friend
mon amie -- my (female) friend
son idée -- her idea (l'ídée is a feminine noun)

Hi Andrew, 

You ask "can son amie be correct"

Amie refers to a friend male or female     https://www.wordreference.com/fren/amie

So I say yes! it is correct.

The text is also correct above "envoyer (qch) à (qqn)

Has this answered you query?

Jim

Andrew, it is always correct - see lesson attached on using possessives followed by vowels or h muet.  https://progress.lawlessfrench.com/my-languages/french/view/132

To be clear, the last example from Chris - “son idée’ - can be either ‘his idea’ or ‘her idea’. The possessive does not indicate the gender of the possessor in this situation, so context is needed to determine this.