Without knowing more there is no way to respond to this specific question. I agree with Ruth Ann. We have good moments and bad moments. It helps me a lot when I remind myself that I love my daughter and she loves me. I have an adult daughter and we exchange angry e-mails from time to time. I've finally decided that e-mail is not an effective way to resolve anything. We have to talk face to face when we are in disagreement. And.....most importantly we have to do this after we've calmed down. It is so easy to read something into the written word that the writer did not intend.
I do gain perspective by talking with an uninvolved friend. Often, I'm able to see a different side to the situation after I've talked with a friend and calmed down myself.
As to adult children being unappreciative I think that it's normal for them to not always appreciate us, especially when we work to hard at being a parent instead of an adult. I found it difficult to stop making suggestions and giving advice. My daughter and I have finally been able to work out our relationship so that she tells me that she doesn't want advice or suggestions; that she just wants me to listen. At first that was difficult. I'm a fixer by nature and by profession. But as long as we remembered that we love each other we are able to work out our relationship.
As to whether or not we feel unappreciated we do have some control over that. We can feel that they don't appreciate us and become angry or we can realize that something is going on between us that needs to be worked out and focus on what we may have done to cause them to act or say something or why we feel this way. It's all too easy to assume hurt feelings when that was not our daughter's intent. Perhaps she feels unappreciated and is putting those feelings on us.
Both need to back off, regain their emotional equilibrium, and find a way to listen to each other. When we're confident in ourselves we are less vulnerable to feelings of being unappreciated. Then we can consider what is going on for the other person.