She has tools to get in, but everyone seems to believe she loses hard to disjoints. My Jigglypuff strategy is basically "Move like they do". As one might expect, with such good air speed and such poor ground speed, the overwhelming majority of her approaches will be aerial, so shields are an invaluable tool against her. After getting Wall of Pained a few too many times way back when, I adopted a shield-heavy mindset. However, camping in a shield alone won't accomplish much, with her air speed it's much too easy for her to drift out of harm's way after an approach. (She also has Pound, but it has so much endlag it's a free punish so she'll want to surprise you with it when your shield's already weakened enough to shatter)
So, I watch her habits and attempt to emulate her movements - if she tries the front of my shield I go for fairly straight jumps and try to hit her with FF Nair/Fair, if she likes to try to land on me or go behind me, I jump backward for the aerial. I tend to prefer full hops, which give me more time to position myself but are more telegraphed, short hops require me to let her get closer before moving, which can get dangerous. Her attacks last quite a long time, which serves her well in hand-to-hand (hand-to-foot? Hand-to-stump?) altercations but keeps her in harm's way against disjoints. As long as I don't let her drag me offstage or hit me with Bair, I've got plenty of time to watch for my chance. I want to work more Bair spacing in there too, but it's quite difficult to aim that hitbox at her.
As for edgeguarding, I... don't. Maybe that's wrong, but in this matchup offstage is Jigglypuff's element and Ike's Kryptonite. Jigglypuff is super mobile and can screw with recoveries almost laughably easy, and if you're out there wasting air jumps and getting yourself in a bad spot, you're throwing away a stock for a super low chance of getting a kill. Better to try and catch her with a tilt or aerial as she floats onstage.
