Adding slab edge insulation on an existing structure

I was asked by a friend (a GC) to visit a home he has been working on. About 2400 sq ft, 14 yrs old. Radiant slab. Had some sort of LP boiler running it, which is now gone, replaced by a 15 kw electric boiler. She belongs to a neighborhood co-op and gets LP at a reasonable rate. She has a VC Defiant wood stove that she likes, but is concerned about lugging wood as she ages. Smart call, I'd say. Solar company said that with the 15 or so PV panels they sold her that she would be in high cotton on the PG&E bill. $700/mo of cotton with occasional use. I asked the owner if she liked the radiant and she replied that she loved it, but due to cost, must abandon the slab. This is a well built place, single story, Loewen windows, etc. The 50kbtu is fine as it heated the place this past winter. She is just NE of Sacramento at 3000' elevation in the foothills of the Sierra. Lovely winters, after the NE;) I much prefer CA winters to summers. After some wrangling the solar company is removing the whole system and putting it back to what was there previously. She will be out the $4500 she paid a local plumber to install the elec boiler, but will get the $20+ k she has in the solar...so she said.

At 2400 sq ft on single story there is a substantial amount of perimeter insulation to be added. So, in your experience, is it worth doing? Insulation type? Installation detail? Flashing? It seems a shame to abandon the slab. The GC is excellent and would do a good job on this. I will observe from a distance;) Any suggestions would be gratefully received!