Hmm well, this is interesting, but since you aren't sure what it's making you feel this way, i'm afraid there's nothing i can really do about it.I really don't like criticizing art done by others (as I have no skill at all in this field), but there is something that bug me in the Murella portrait.
She's very cute, but she doesn't look like a very shy young girl anymore. I don't know how to explain why, it's just a feeling.
In fact with the 2 new portraits, I feel like Selene is more shy than Murella.
About the only thing i could think of were the anime tropes for eye shapes influencing your perception, but i fear tweaking it doesn't make much of difference at the resolution of these portraits:

In any case, i feel that the game itself makes a convincing enough show of portraying Murella as a shy girl, that a quite generic portrait doesn't really have enough power to contradict. But, well.