Purchasing a Scroll of Fly to add to her book.

3rd level scroll 375gp

Fails to write the scroll to her book, purchases another one.

Total = 750gp.

I have added a Scroll of Fly to your character sheet for the listed price of 375 gp. As per the rules for adding spells to a wizard's spellbook, you don't have to purchase the scroll a second time:

If the check fails, the wizard cannot understand or copy the spell. He cannot attempt to learn or copy that spell again until one week has passed. If the spell was from a scroll, a failed Spellcraft check does not cause the spell to vanish.

Additionally, since the failed check applies to understanding the spell, and that step happens before writing the spell into your spellbook, the cost to write it does not apply yet.

You can roll again Oktober 15th, and if you succeed, you need to pay 90 gp to add it to your spellbook, and the fly scroll will be used up. That's still cheaper than 2 scrolls ^_^