Maybe the Frankenstein bothers her because it is more similar to a person? My daughter never could stand dolls, except for Barbies, which were so small that they couldn't be confused with a person. Otherwise, dolls frightened her.
Also, you said she likes music, but if you notice, the Frankenstein doesn't sing so much as he raps. He is less musical in that way.
When my boys were little, we lived in an upstairs apartment. My Halloween decorating consisted of a jack-o-lantern outside. We would TOT on a nearby street where people went all out for the festivities, but my older boy (the only one old enough to participate back then) got into it pretty quickly when he saw all the other children and the candy.
I started doing more decorating when we moved to a house, but by then my older boy was 5 and knew the score. I think the younger kids followed his cues.
My daughter (now 17) loves Halloween cute, but is turned off by Halloween gruesome. Middle son seems more or less indifferent, except to the candy. Older son, who is on his own now, has been known to throw a Halloween party or two. He is like me and enjoys all holidays.