Would de-sensitisation help ? Try and work on different levels:
ie. working together to cook / bake something using an oven, helping each other clean an oven a bit etc. looking at nice ovens in a store etc. etc.
discussing which bonfire celebration to go to, and what will happen, how big will the bonfire be at the end etc.
running through evacuation procedure for smoke alarms, and maybe testing 'the plan' several times one afternoon, with the alarm, so the 'concept' of a fire happening, and the noise of the alarms etc. causes a constructive 'get out / get help' rather than 'mum's gonna get hurt' etc. etc.
Plan together what some of the bits of the new kitchen might be - little things like she gets to choose the tea towels, or have a special Disney character on a tile etc. etc. etc. so she looks forward to any redecoration works / refitting ???
Dunno... just thinking aloud....
It could be that it would be best to figure out what you want to put the oven fire down to IYSWIM... rather than her fearing 'electric appliances may spontaneoulsy combust' it might be more 'understandable' (logical ?) to conclude it was excess fat left in the grill or sommit... (again, just thinking aloud... maybe some would argue she'd need to understand 'sh*t happens' / random bad things can happen etc)...
HTH