I am a firm believer in spaying/neutering your dogs. I have both a female and a male and have never seen a difference in their behaviour. My female was spayed at 6 months and my male was neutered older because he was a rescue. After you have your dog spayed, you don't have to worry about any accidental breedings and the mess.
spaying as soon as you can(since she is 8months), is the best thing you can do for her. I have had both boys and girls, and I do breed. I have found that at least in my mini aussies, they are so much more loving once all those hormones are gone. In tact dogs can be way more agressive, and girls can be sooo moody.