I won't get into
why she needs to find help (and yes, I do hold a masters degree in social work if you would like to question or challenge my credentials or level of education).
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You have never spoken to her - you have never seen her - you have never interviewed her - so the mere fact that you have a masters degree does not put you in a position of being able to "diagnose" what may or may not be "wrong" with her..
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From my post, I am simply hoping that SOMEONE who knows her will heed my advice and take action.
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The OP of this post is her sister - who I would assume is in a much better position of making a diagnosis (if one is needed) and/or making decisions as to whether she requires "professional help" than you, me, or anyone else here..
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Her behavior may be triggered by psychological trauma suffered as a result from the loss of her husband. It could also be environmental, and bringing her to the very place where she shared memories with her husband might only be enabling and flaming the illness.
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This is not "new" behavior.. This has been her enjoyment prior to her DH's passing as well.. And from what I understand, he would often accompany her and found it rather enjoyable himself.. They both simply enjoyed Disney World.. 
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As to her repetitive coping mechanisms-
eccentric clothes, wig, makeup, nails, garbage bags filled with old bears, ritualized behavior she feels compelled to perform each day, etc..