My issue is, the OP keeps stressing (for those of us who must not know?) that "I satnds for interstate" - which appears to actually have little, if any, importance in the actual incident or discussion. More accurate and informative may have been that it's a limited access highway.
I'd still like to know why this excellent and experienced driver didn't use her directional when merging into the highway, and what happened to that fourth lane. Oh, and I'm also not clear on where, exactly, she saw the other driver's headlights. In her rear view mirror seated in her natural/normal driving position, great; any other way - straining to see in the rear view, using a side view mirror, craning her head left? Nope.