Hmnm, I seem to remember in my studies that ZSS doesn't suffer any shield hitlag from Dsmash at all (one of the reasons the move is so safe), which would define Dsmash as a projectile. Apparently though, my studies have failed me in this regard, so I apologize for anyone I've mislead.
TIME TO GO DO MORE RESEARCH!!
You should ask the lab before you say something questionable, like I always do.
Dsmash is a projectile with no trajectory or velocity, which means it doesn't move, which means multiplying the speed or changing the angle (i.e. reflecting) sends it exactly nowhere. Since damage/kb from a move is calculated after the move is reflected, characters with reflectors aren't hit by moves they reflect. Since ZSS' dsmash is never really reflected to begin with (because the multipliers that change its' direction don't apply, 0xN=0 etc) the opponent is still hit by the attack.
The confusing thing for people is that ZSS' hitbubbles for dsmash actually do touch her(and touch behind her as well) but don't damage or stun her. I would guess this is because projectiles can't damage the person who creates them unless the angle/velocity is changed mid-launch, or unless they create another article on their own (Snake's nades exploding, etc).
Projectiles don't work the way you think they do.
Projectiles is pretty arbitrary of a term, as Brawl does not define projectiles. The game rather, uses articles as something that isn't directly an attack from a character. This includes things like Snake's D-smash Mine, Lucas' PK-Fire and ZSS Paralyzer. (note: Grenades, Bananas, Gyros and Turnips are considered items). Some of these can be reflected or absorbed, some can't. It depends on if a bit in the specials flag is set. This bit is also found on some attacks that aren't considered articles. This includes things like ZSS D-smash and Pikachu's Thunder (the part where he hits himself). However, in ZSS D-smash, the reflection bit is not set, therefore, you cannot actually reflect the hitbox back at ZSS. You can only absorb it because a different bit is set.
Now, when we actually look at the bit in question, we can define it's actual properties. Here is ZSS's D-smash Special Hitbox Flag:
014FFFC0
0000 000
1 0100 1111 1111 1111 1100 0000
The top number is the number in Hexadecimal as it appears and is read, the bottom number is the binary bits that we can understand (see:
Salute to the Flags). The first bolded bit (bit 8) determines if the hitbox can be absorbed. Since it is set to 1 (meaning on) it can be. The next bolded bit is the reflectability. It is set to 0 (meaning off). The means, without any doubt, that her hitbox cannot be reflected.
Sorry about the rant... I just dislike when my labbers get info wrong b/c they don't consult another member...
Peach and Sheik I would switch around though, along with Mario and Shelda. 
