Is it permissible not to place the deceased on their right side, and what is required after 21 days have passed since the death?

You are not required to exhume the grave because you already alerted those responsible for the burial. This is considered a Sunnah (definition) (recommended practice), and while some scholars have deemed it obligatory, the more preponderant view is that it is not obligatory. You should supplicate for her, seek forgiveness for her, and give charity on her behalf. Even if it were considered obligatory, the grave should only be exhumed if it was soon after the burial, making it highly probable that the deceased's body has not changed; otherwise, it should not be exhumed.