I habe a seven year old border collie and i'm planning on bringing home a new 8 week old kitten, should I be worried if my dog will act out and hurt her? My dog is sweet but protective, I just don't want to take any chances.
Is your dog used to cats? Collies aren't the easiest breed to integrate with cats (though I have friends who've successfully managed it). If your dog has never lived with cats before, I'd say that 7 might be a little old to learn. If you're dead set on a cat, then you'd be safer getting an older cat that has previously lived with dogs imo. What's needed is a cat that will stand it's ground and not act like prey.
However, if your dog has grown up around cats then a kitten should be fine - just so long as introductions are done slowly and carefully.