Tbh Avril on the Other Stage, in that slot, was always asking for trouble. It's not just the migration, but the field itself was by far the busiest I've ever seen. This isn't hindsight talking, given that it panned out exactly how many people including myself predicted from early on. Put her on at the same time on Saturday (so up against Michael Kiwanuka) and you'd get the same effect.
She should only ever have been booked on the Pyramid given that she's exactly the kind of act that always attracts a huge crowd at Glastonbury. Even in a "normal" year against stronger competition it would have been very poor placement. It's a poor decision by the Festival on all counts - for all artists involved, and for customers as well.