It can take the iPad a few seconds to catch up with what is on the server. My emails often s how unread for up to half a minute before they update. Emails deleted on the Mac may take that long to be removed from the iPad's inbox as well.
If all else fails, try taping the reload icon at the bottom of the inbox
Also, go into Settings >> Mail, Contacts, Calendars and make sure the account is set for push. Go all the way to the advanced settings to be sure.