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I find it difficult to respond to your message with the details that you have given.
Not everyone who is ENFP has high self esteem. All that I have ever met have been enthusiastic, but I have not met any that I have considered selfish, although all were selfish in regards to certain things, myself included. Perhaps this is a trait of your particular ENFP, or perhaps you are speaking in regards to a particular thing. If your ENFP used to have high self esteem and now she seems not to, perhaps something has happened to make her question what she thought was a strength? Again, since I do not know the particulars, I cannot speculate.
As far as her enthusiasm goes, something must have happened. During times of great trouble, my enthusiasm has waned. After the death of my grandmother, I had a hard time. In time, I became more enthusiastic again, but people do change over time. Without knowing why she is withdrawing, it is hard to tell.
I'm sorry that I do not have answers for you, but I feel like without more knowledge of your particular situation, I would be giving you bad information anyway.