Dog problem

I have a cat aged 10. Then a female dog now 5 then a cat nearly 5 and a female puppy of 6 months. The older dog for the first 2 years was reasonably well behaved and tolerant of the cats and very social with other dogs. Over the last few years her behaviour has deteriorated in that she wont stop chasing the cats and cant be left alone with them for fear of her attacking them. They run at the sight of her and this makes matters worse. On a couple of occasions she has caught one or other and drawn blood. She is ok with the puppy outside but will go for her in the house so they have to be kept apart. I see her problem as jealousy as she also attacked a friends dog for coming too close to me. Basically I don't trust her and don't believe she can be rehomed. Tonight she chased and attacked one of the cats again pinning her down until I screamed and she stopped. I'm thinking my only option is euthanasia which breaks my heart. I have grandchildren who live abroad but when they visit I have to kennel the dog for fear of her unpredictable behaviour. The feelings of guilt are enormous but how long before something catastrophic happens?