Hm...
The first time and pretty much the only time I've even fought ZSS was at my first tournament ever (about 1 month ago), and I have to say ZSS is a hard match-up for Jigglypuff.
As for me, I "semi" like to play in a way that I'm constantly spacing my bairs to force my opponents to charge at me so I can grab them and/or punish them. Of course I mix up my styles, but I like doing this style the most :D
ZSS has the potential to be a powerful tank against Jigglypuff. Which makes it difficult because now I must charge in and avoid being punished and/or shield grabbed.
At the get go, ZSS already has her armor to throw right in your face, and then right after she can just stand there shooting those small bursts of stun gun things right at you, forcing you to either shield, jump over it, side-step, or run away. As for me, I normally just jump over it. Reason being, to look like I'm helpless in the air so that the person I'm challenging will charge in so that I can punish them for doing so (shield grabbing oh how I love you so).
When approaching ZSS, she has the tools to push you away and the hitbox range to hit Jiggs before you can hit her. With moves such as her forward special, up special, and most of her smashes (her up smash and up special is that exact same thing...wth).
A good thing within all these negatives is that there is an angle where we can jump in and attack and still avoid everything she can throw at us. The bad side is, if the player playing ZSS realizes this and uses that weakness to bait and punish us Jigglypuff mains.
Another good thing is that ZSS has a lot lag time after her move is done. That will be easily punishable from pretty much anything, like resting :D
As for gimping, I'd say it's not hard, but not too easy to gimp her. I'll say it's easier to edge hog her than to gimp her, but I believe this area can be widely argued upon.
My advice on how to approach ZSS is to force ZSS to move (In other words play campy and defensively). I feel that you'll have an easier time fighting a moving ZSS then a tank ZSS. Being that it will be easier to punish ZSS when she's moving because of the lag after her moves. The tank ZSS will just end up with you jumping in and being punished for doing so.
So use that angle where you can hit her but she can't hit you to make her move around.
How to use that angle? I think you could just mix in attacks and empty short hops to confuse and bait your opponent, thus making them move.
Though I'm new to the boards (this being my second post ever), this is my opinion on the matter of ZSS and Jiggs. Of course my mind can be swayed be other opinions if I feel they dominate my beliefs.