It's understandable that a mouse who's really a child is scared of a fall. However, there are also several instances of mice needing to be saved during a fall, or being cushioned from a fall - when in fact mice cannot be hurt by a fall, since they are so tiny they descend slowly due to air resistance.
Mrs Jenkins face looks CGI'ed at the end when Granny is talking to her.
Near the end at 1 hour 34 min Hero mouse references to Mary as Daisy although he learned earlier in the movie her real name and commented on it that it's pretty.