Searched to see if this had come up before, but couldn't find anything on here.

Situation:
I am Lifetime Plat
Me, wife, daughter and daughters best friend (both 18) are traveling PHX - OCG next Sunday, July 8th. Paying for the all the seats. Went to buy 2 first seats for me and wife and 2 coach for daughter/friend. Couldn't figure out how to do it on-line so called the Plat line. Agent told me that I would have to make two separate reservations. Fine with me, but when I asked her if I would be able to put my daughter/friend in Main Cabin Extra Seats without having to pay additional (as I would if all four of us were in coach) she said no.

Is that correct? Am I missing a trick here?

Thank you