- Heater itself: tungten wire wrapped on ceramics? Sealed tungsten unit as found in hot water pots? Oven rods? Electric stove coils? Lamp-heated? Etc. What exactly do you intend here?
- Oven chamber: If lamp-heated, then nickel plated is cheapest, though gold plated is better. If convective, any material may suffice.
- Insulation and/or Cooling: Regardless, you may want to use insulating materials between the inner walls and anything your daughter might touch. There are a variety of materials (ceramics, and any number of other options.) If lamp-heated, you may want to consider a simple quartz water cooling jacket.
- Closed loop control system. Obvious.
- Protection: GFCI, door inter-locks, bimetal thermal breaker, over-current, iover-voltage, etc.
I've built a home FAB oven that was lamp-heated and used a quartz-jacket water cooled system with nickel chamber inner walls and which used a PID closed loop control system and non-contact temperature measurement. Thousands of dollars invested in that. And it worked to develop 300 C per second ramp rates. But there is no way this was safe for a "daughter" to use.
Despite that experience, I've no idea what to recommend for you. You haven't disclosed WHY you are taking this route instead of just buying something relatively cheap, tested, and ready-to-use. There are too many good/useful products out there right now which already do all that you need and do it for a very, very reasonable price. Home-brewing this just seems very odd, unless you have some driving reason that you haven't stated.
That said, do take a look at the products available from Cotronics. They aren't a solution, but they do provide unusually useful products that may be part of one. If I were crazy enough to consider what you are considering and had some driving reason of my own, I'd probably go there are part of my research.
Speaking of which... what research have you actually done on this? Beyond just finding a heater, I mean?