I think 8 month is very early. I have an 18 month old who barely knows how to use a fork, not to even mention spoon. I think they learn faster with the fork, it's a little easier, then after she learned that I will teach her the spoon. But at 8 month is too early in my opinion.
Just let her experiment. Its not too early at all. My daughter was about 8 months old when she would take the spoon out of my hand, put it in her mouth, and hand it back to me for more. If its warm where you live then take the highchair out on the porch and let her try out there, that way you dont have as much of a mess. Oh, and make sure to have her only wear a onesie or just a diaper! Good luck :)