I am sorry that you feel bad for such an immoral action. But we cannot do anything in this situation against the answerer.
As a community member, you should not feel bad now because you have 8k points in the site which itself shows your positive inputs to the community. But Rita is a starter and we should appreciate her efforts to answer the question.
Here the "immoral" behavior came from the OP in my opinion. He resolved his issue from your answer and hence accepted it. Then he just gives credits to Rita's answer. There may be multiple reasons for that. It may be due to:
- Rita may be his friend.
- He felt that Rita's answer is more descriptive than yours and thought that answer is better than yours (in later stage).
- etc etc.
As you can see, reasons are plenty. Suppose the second one is OP's reason to accept her answer, does it become immoral? It's a question that we need to ask ourself.
The point here is, you are doing well here and you should always try to be a good community member. Good community member always improves the content of this site and always have a positive approach to any action. A good community member also encourages other community members for their contribution.
If they did anything wrong or immoral, then you should guide them and tell them through a comment that it is not what we expect from a community behavior.
We are not here to teach others morality, but help each other and improve the content of this site.
So emotions aside... a positive and a helping mentality beside. :)