Everyone gets a sore ass in 45 minutes on the stock seat ... but we aren't sitting right behind you (whining).
Try beads to make it 'bumpy'. Try Sheepskin to make it 'cushy'. Try Airhawk to make it 'floaty'. Try someone elses 'custom' to get her more input...
but ultimately you'll get a custom seat. I like Bill Mayer and Seth Lamm. Both are cheaper but similar to the bucket seat sold by Russell (A+).
Posts some pics of her ass and we can make even better recommendations. (That's what the pros say too).