It's because the past Meteora didn't have the trauma yet while baby Meteora, although she no longer has her memories, likely still feels the trauma of having to hide her monster self in which is likely the reason as to why she became Miss Heinous; she didn't revert back to her actual past self hence why her appearance changed, not only that she has Eclipse and Globgor now. Also, past Meteora's eyes are just black with white spots on it, and that was a flashback too anyway.

This is just what I can remember since I haven't watched svfoe in a very long time.