There are certain verbs that are rarely used in continuous (progressive) forms. For example, we wouldn't usually say, "I am having a nice house," or, "I am believing what you say," or, "I am liking this music." (Instead, we would say, of course, "I have a nice house", "I believe what you say", and "I like this music".) The verb "to be" is in this category. So we wouldn't usually use the continuous form to describe a basic characteristic of something (e.g. "His house was being big," or, "My work was being very interesting," or indeed, "She is being beautiful.").
However, it is possible to use the verb 'to be' in the continuous form in some situations, for example when it's a temporary situation that continues for a short time. For instance, "You are being very silly. Stop it!" or "I'm afraid they are not being very cooperative at the moment".
I'm not sure if I've answered your question, but I hope it helps.