My boyfriends dog killed my kitten

A little background:
My dog is a sweet staffy and had her for 5 years and my boyfriend has had her for 8. She’s a very reactive dog but has never shown signs of aggression towards cats in the past. About a month ago my boyfriend and I took in 2 stray kittens from outside (about 2 weeks old) our dog did great around them and often acted like a “parent” with them. As they got around the one month mark our dog would keep them off the curtains and away from the tv she would do this by going up to them, tail wagging, and butting her head into them. The cats would swat at her but she never reacted badly. We did have to feed the cats and the dog separately due to our dog feeling territorial over her food.

Night of:
It was a normal day and our dog was playing with the kittens as normal. Later that night it had been raining and I had to take our dog outside. I brought her back in and wiped off her paws (she hates her paws being cleaned but tolerates it) one of our kittens was in front of our dog while cleaning her paws and I was turned away so I didn’t notice our kitten was in front of the dog. Our dog snapped at her and our kitten made a noise and I turned around and she was instantly seizing. There was a lot of blood and her eye was dislodged from her head. We believe this was an accident on our dog’s behalf because our dog immediately stepped back and was inspecting our seizing cat and was butting her nose at her. It wasn’t prey driven at all. We talked with the vet and the vet said it was one bite in the head and the pressure of the bite is what had killed her. My boyfriend and I have been in shambles since then and going through what if’s and feeling immense guilt. We are unsure if we should rehome our dog, take her to the humane society, or rehome the other kitten. They both are the absolute sweetest and we believe this was just a really unfortunate situation with bad timing. Would it be irresponsible to keep both our dog and kitten? If we do keep them both my boyfriend and I would be extremely cautious with them both being in the same room and they would never go unsupervised.

Any advice is appreciated :)