My wife and I got our cat when she was a kitten. She's about a year and a half old the dog is about seven. They have got along fine till today. One min. she's fine the next min she freaks out and starts attacking the dog. The only thing I can think of is, I think she's going into heat, but she's never acted this oddly before. Are her hormons just out of wack or could it be something different. I have locked in the spare bed room to keep them separate till I figure this out. Any info would help Thank you

Kitty is maturing and not so playful any more. Perhaps the dog still wants to play & bugged the cat?
Or else the cat was in a bad "mood" and just decided to take it out on the dog.
Since the kitten grew up with the dog it may just be a temporary thing. Try letting the cat out again to see what she does.
Cats get "jealous" too. This happened when I brought a kitten home: my female cat was so jealous she refused to eat for two days.
Sometimes a dog will "over-react". It must have scared your dog for the sudden change in behavior, so he or she probably yelped loudly. If the cat goes after him or her again, your dog will learn to avoid her.
I have two other cats that are male. The older one picks on the younger one all the time, even though the younger one could kick his butt. It's all part of the "game" of showing: "I'm number 1 around here".
Lots of possibilities here, you have to figure out which one it is.

It is probably having a hormonial act up and is misbehaving because of it. Keep the two separate for a while, to see if she settles down. If she is still acting up in a week or so, call the vet. Good luck