Tabitha experienced a vision in S3E9 of Miranda's death less like a vision and more like a memory of something she personally experienced. The S3 finale confirmed: Tabitha is Miranda, Victor's mother, returned.
After S4E6
Tabitha was largely peripheral. Whether she re-enters the active investigation will probably determine whether her Miranda memories become useful or remain backstory.
What's confirmed in canon
S3E9Experiences Miranda's death as personal memory.
S3 finaleLullaby confirms reincarnation.
Pre-FromvilleMiranda was Victor's mother. Hid Victor and Eloise in the root cellar the night she died.
S3Briefly escaped Fromville via the lighthouse, found in Camden, Maine, returned.
Where the community lands
Reveal canon. Open: Miranda's choices, what she knew, where Eloise went.
Still open
Q1What was Miranda protecting Victor from?
Q2Where did Eloise go?
Q3Is Victor's father alive in Camden?
Q4Why is Jim in town but not a reincarnation? Jim was killed by MIY in S3 finale. His ghost may not be his soul.
Connected entities