Here is the full list of all 14 Millie achievements.
Complete 3 levels in a row without restarting or going back to menu
Reach the aviation school
Use the teleport 20 times in one level
Guide Millie through 4 differently coloured teleports at the same time
Use the scissors 10 times in one level
Make 10 turns on ice in one level
Use the clock 10 times in one level
Finish 8 of flying levels with 3 stars
Complete the whole episode with 3 stars in every level
Collect all possible shoes in the whole episode
Forcefully enter the one way street 5 times in one level using the beacon light
Complete 5 levels within maximum time
Use 3 distinct hammers on 3 distinct chipped walls in one level
Finish 5 levels without using the clock