Do you remember the episode? It seems like it would be Aiden and not Angell, as I cannot recall any episode where Stella actually spoke to Angell. Especially not about Mac. It would be more realistic if it was Aiden. But as I don't know what you are talking about, I can only guess.
I think what hotspot might be referring to is when Angell was helping Stella with that Greek coin investigation against Mac's wishes. They did mention Mac not knowing what they were doing.
I do see Stella as being kind of big sister-ish to Lindsay and to some extent to Danny too.