When she was going to have her own show, she was a plant!
The show was going to be forest/plant-elf girl vs pollution demon wizard man, originally. Environmentalism, "Captain Planet" and all that were popular themes to push at the time, so why not develop that sort of a show? An action piece, but with a female lead for Saturday mornings. It made perfect sense at the time. And what to better represent "Anti Forest Destruction", than a literal part of the forest? There are ever-present leaf elbows or gauntlets, and leaf/grassy hair-dos galore. What's a bit of a shame is none of them have colors set in.
Baseball Cap Hairdo
This one wouldn't work because the face wouldn't be visible from the front/camera always needs placed under her to see the face.It has a floral cape and "Her own Sonic Sneakers", so they were thinking about giving this one his speed. This one is the oddest as the face is the most obscured and it is nose-less It is the most 'monsterous' of them.
Bubbling Spring Hairdo
This design looks like it's out of the Jetsons/retro/future somehow. It has a skin-tight leotard with big 'space collar', thigh-high boots and the elbow leaves. She is otherwise 'human'. This one is an adult with a chip of cleavage and nearly leering eyes.
Tree Head Sally
Bottom left art, this one they're evolving into each other as sketches and ideas are absolutely supposed to do. You've got the elf shoes and leaf elbows but the hair-do is evolving into a flowering tree.
Long Hair Sally
More Sonic Sneakers, but the Jetsons' collar is toned down & now her headband is plants. This one has more of human body proportions, although all designs use the "Big Head" method.
Witch Hat Sally (Far right)
Whoever did this is a DIFFERENT artist from all the rest here. And...despite it being a tiny human, you can see that this exact one is the one that became Sally. They crossed her with the Princess Jasmine Bear next to her, and that's what they got. She's got the right hair (big bangs), the proportions (head body ratio), the large-er feet, and even the eye shape is starting to be there.
What's super interesting about this one is that it is actually more Sonic-like than she ended up being. The shoes are very Sonic-character-esque, as are the big-hand gloves and the 'stick type / noodle type' arms. There is the "Female-styling-shape" for the torso & limbs, but it is less than what Sally actually ended up with---thus putting her more in-style than out of it.
Sally Cat-
This came out of left-field, especially because it was published promo-art. It doesn't fit with anything else, and also not into the design timeline. Unsurprisingly it's unpopular with anybody who sees it because it doesn't make sense and is full of cliches. Random evening-gown! Cleavage! The cat is yellow because it is blonde-haired person because blonde hair is best hair color! It is princess because how is female valuble if not royalty!? Wears crown all the time despite making no sense to do so! Enormous human lips with lipstick! Kiss men!

But what all of these don't do?
Look like they fit into the Sonic universe. Keep that space elf in mind too for Antoine later on...
What do all of them EXCEPT the human do?
Take an action (run/point) or regard the viewer. Every design except the human is preparing that character to be 'a main character'.
Take a Guess
I bet that she was green. Probably all of them had green skin and hair.