The music makes you get a feel for the enviornment and times the story takes place in. Anything else in my opinion would sound awkward and unfitting.
As for people who think Horo's acting strange, I don't see it. Whenever she broke down in the last season certain emotions and traits you wouldn't expect or regularly see from her were fleshed out. She stumbles and falters when her own emotions get the better of her. I find that no different than what happened in this OVA. She is obviously concerned and her actions reflected that.
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