She is from the blood group B and when her kittens are type A they are doomed to die :
Any antibodies present in the blood of a queen (female cat) will also be passed into her milk and colostrum (the first milk produced) if they are feeding a litter of kittens. During the first 24 hours of life, a kitten's intestine is specially adapted to be able to absorb these antibodies so that the kittens can acquire 'passive protection' from the queen - ie, the absorbed antibodies will help protect the kitten against diseases in the early weeks of life.
This process is highly beneficial for the kitten, but it can sometimes cause problems with blood groups and blood incompatibilities. If the queen is of blood group B, she will have naturally-occurring anti-A antibodies. If she is mated to a type A tom cat, some of the resulting kittens will be type A and when they feed on the queen's milk in the first 24 hours of life they will absorb the anti-A antibodies, as well other protective antibodies. The anti-A antibodies will then destroy the kitten's red blood cells just as if there had been an incompatible blood transfusion. This is a condition known as neonatal isoerythrolysis. This can be a significant cause of death in young kittens in certain breeds (especially those with high numbers of both type A and type B cats).
This disease does not occur in type B kittens born to a type A queen, as type A cats have much lower levels of antibodies against the type B blood cells and often no antibodies at all.
I saw all these symptoms :
Sudden death, with no prior warning signs in some kittens
Most affected kittens will appear to 'fade' over a few days - they will stop suckling from the queen, become weak, often appear pale and may become jaundiced (yellow)
Affected kittens usually pass red coloured urine, due the presence of haemoglobin (released from the breakdown of red blood cells) in the urine
The one who survived last summer is probably type B.
These link explains everything and is interesting :
https://icatcare.org/advice/cat-health/ ... patibility