I think the answer depends on: why is it necessary, for the survival of the young, that the mother burst into flames?
If it's not necessary, then it becomes difficult to explain how this species would have ever evolved to do this.
If it's necessary simply for the heat given off to make the eggshells crack, similar to pinus contorta (the pine whose seeds only hatch when heat from a wildfire), then you have to explain A) why wouldn't the mother just breathe fire or something like that instead of actually consuming her? Not having the mother around to protect the young is a big disadvantage. B) what would be the evolutionary advantage of only having a species hatch in the presence of fire? In the case of the pine tree, it exists in a biome where wildfires regularly kill all the trees, so this is its survival mechanism for the species. But if it's the mother breathing the fire, this reason doesn't work.
Now maybe you go a different route: it's necessary for the survival of the young so they can eat the mother's ashes, because they have vital nutrients.
The problem with that would be that there's little nutrient left in ash, most importantly no proteins, which are vital for young who need to grow a lot. From the wiki page on cremation, specifically about the composition of the ashes left behind:
Cremated remains are mostly dry calcium phosphates with some minor
minerals, such as salts of sodium and potassium. Sulfur and most
carbon are driven off as oxidized gases during the process, although a
relatively small amount of carbon may remain as carbonate.
The augmentation that I'm seeing as viable is something like pinus contorta, where there are regular wildfires in the region, and these wildfires consume the mother but hatch the young. She lays eggs and they simply lie dormant until a fire comes along to hatch them.