Is Avril older than Pippin? Or are they litter mates?
If its the latter, being older and more mellow, also the more experienced.. When Fudge died, Treacle who is over half her age younger (2 and a half) became a lot quieter, but never gets bullied by Liquorice who succeeded Fudge as the boss when she passed on..
BonBon on the otherhand, although now 6 months old, really wants that job, and can be really aggressive towards Liquorice, who will not back down, and only this week, has managed to put the little white fur ball in her place..
The boys.. their stories pretty much the same.. Tickles, my huge Abyssinian male, passed away 18 months ago, leaving Crackers distraught, as they'd been best buddies, despite humping each other all the time... his personality has changed completely, and is reminded of who is boss nearly everyday by his companion, Biscuit, but neither is aggressive, its all just hyped up play, a bit one sided, as Crackers wont play ball
Perhaps get another female, to pal up with Avril? Try and get a mellow one, who compliments her personality.. you might find that a sweet natured pal will help Avril become the piggie you know
Perhaps a threesome? my girls seem to cope with that arrangement