I'm always amazed at how objective and rational any characters are expected to act when they're in the grip of their emotions, let alone very young people, let alone young people in a relationship--"right" and "wrong" get weighed in the scales of justice by readers acting like Grand Inquisitors.
More often than not, both parties are partly right and partly wrong, so all this parsing out who should really apologize just replicates the argument in the story--the point is that (as is normally the case in garden-variety domestic arguments), they're both sorry they ended up fighting and want a way out of it.
To hear some readers you'd think we're the judge and jury in some kind of moral small-claims court.
Nanoha is the one who tends to wear her emotions on her sleeve, and Chidori is the more tamped-down one. That's always been their basic dynamic--as the friend says, they usually bring out the best in each other. But occasionally, temporarily, it works the other way.