Necrosis is one of the risks with laser-assisted liposuction.
If the liposuction was performed very recently, the burns may still improve a little by themselves.
If your friend ended up with fat-necrosis (death of fat cells) below the skin, it is unfixable by dermarolling because dermarolling can only affect the skin itself and not the structures below it - such as fat. Are the burnt areas indented? I think the surgeon who performed the liposuction should inject the indentations with temporary or permanent (risk of uneven skin or nodules) filler. The best long lasting and relatively risk-free filler is injecting her own fat into the indented areas but I am not a plastic surgeon and I do not know whether it is suitable or possible in this case. Fillers will not improve the scars but they will improve the indentations.
If the indentation is not caused solely by fat necrosis but also by the skin scar being anchored to the underlying structures (which often happens in burn scars), needling or targeted dermarolling of the scar will help releasing it.
Skin scars that resulted from burns can be improved by dermarolling or needling. It will soften the scar, improve its color and perhaps slowly rebuild some of the skin tissue that is missing.
Depending how wide the scars are, your friend should buy a 1.5 mm ONE LINER roller (if the scars are very narrow lines) or a 1.5 mm NARROW roller (this roller has three lines of needles - for wider scars).
If the scars are not elongated (line-shaped) but more like a circular, oval, square etc shape: Buy a 1.5 mm dermastamp.