Bison as an animal companion

[Korlos]

My girlfriend is playing a barbarian with the Mounted Fury archetype. In this region, bison are very common and she already has a mundane bison as a mount. When she gets to 5th level, she will more than likely want a bison for her Beastial Mount ability.

For effective druid level 1, she would combine the companion stats for aurochs or bison with the 1st level row on the druid animal companion table, right? When do you use the "7th level advancement" block? Do you apply those modifiers at effective druid 7?

[Talonhawke]

Yes and Yes as far as I can tell.

[Lord Twitchiopolis]

Keep in mind the feat Boon Companion if you're looking to get a stronger pet. It raises your effective druid level by 4, to a max of your level.

But yes, you would use the effective druid lvl 1 stats at 5th and apply the 7th lvl advance at 11th otherwise.