That was such a tragic event. In a way I could see why the Queen may have waited or was advised to wait to visit eight days post accident. The immediate aftermath and rescue/efforts are going on and to visit right away could hamper/deter those efforts.
I'm not saying HM wasn't aware of this, but the press, even in 1966 was apt to be critical if HM did show up immediately after the tragedy.
I remember watching the coverage when HM and Prince Philip visited the site and both were deeply affected.