A lot of it is knowing what ranges you want to keep yourself at. At far distances, you can actually trade cr.fierce with her jump attacks and it’ll trade in your favor. At medium range distance, she has a bit of an advantage. She can jump over your sonic boom on reaction and beat a lot of your standard anti-airs clean, which lets to putting you in a mixup situation against Chun’s pressure. This is never a good thing. Closer than that, you force her to either use fireballs or walk forward to close the gap. You can match fireballs to maintan neutral frame advantage, or she throws a really late fireball to match yours, you can follow up with a backfist. This is the perfect range to be at, since if she jumps, if you have fast reactions, you’re actually able to walk underneath her and hit her from the other side. This is a pretty crucial skill that I don’t see a lot of Guiles doing.
God help you if you fight a Chun who actually knows how to properly turtle and build up meter asap. Then it comes a headache.