Petrana: In her head, and probably in reality, Morgana will always refer to her as the Countess -- as the use of a title, in her canon, implies a deep respect. Besides the appreciation earned from helping Morgana during her first hours in Taxon, Petrana is something Morgana's never had in her life: a more mature woman who has (or appears to, Morgana doesn't know but appreciates both skills) her act together. Having never had that type of a female presence in her life, Morgana's bonded to Petrana extremely quickly.

This would be the reason Morgana's stayed away from Gatas. Having grown up the way she's grown up, she knows that outright affection is often treated with awkwardness or condescension (on Uther's part) or ridicule (Arthur's). Naturally, this belief will be transferred to Petrana.

In short, Petrana is her absolute favourite person she's met thus far in Taxon.