No it’s the right preposition (I think that’s the right technical term here!).
We are using ‘air’ = on.
But we do NOT need to say ‘oirre’/‘on HER’ because we say Mairead explicitly.
So we just use base ‘air’.
(...although confusingly also ‘air’ = air + e = on him - we are not using that sense here).
The full list is given in tips for Feelings 2...
... or ALL tips listed here! https://duonotes.fandom.com/wiki/Scottish_Gaelic
Saying (this is WRONG but to explain) ‘tha falt bàn oirre Mairead” = the fair hair is on her Margaret, ie we don’t need ‘her’ AND ‘Margaret’!
She has fair hair = tha falt bàn oirre (ie. air + i = oirre)
Margaret has fair hair = tha falt bàn air Mairead (ie. air + Mairead)