From a technical standpoint, that would make her play and feel just like Sonic did in Sonic 4. Hills and slopes are designed in a way to facilitate the speed and momentum gain thus allowing a character to get through the level. If this is off, then you have to place speed boosters or (in the case of Sonic Advance) floating platforms to bypass the lack of speed. I understand wanting the "slower Amy" aspect from a canon perspective but Sonic Team themselves threw that out the window with Advance 2 & Heroes. The only compromise would be to give Amy Roller skates or something like that to supplement her lack of athleticism. Slower acceleration + Speed cap = Sonic 4