Desperate me-ouch!!

I have 2 indoor cats,(pic included)both females,the oldest has been fixed and declawed.the youngest has not.they've been together for about 2 years and always loved each other except for their occasional playing..last saturday the youngest flipped out and attacked the other !!!twice!!we immediately seperated them...whats going on?then this morning thinking they had time to cool off we let them both out together the minute the youngest one laid her eyes on the other she attacked!I thought she was going to kill her!what's wrong?why such a sudden turn?what do I do?I plan on having her fixed soon,but will that help???I don't really want to get rid of her either..please help

Is she in heat?? Could she be pregnant? There's some sort of territorial 'thing' happening here...Get that young cat fixed!!

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FIXED !! right away!

But will having her fixed help?Should the older cat want to get along with her after being attacked?Thanks for advice..