To get Yue Ying you have to win Wu Zhang Plains on the Wei side after taking her and Guan Ping out for the first Target. If you want to do all of them at once, have a fast horse, take out all the generals who are marching on your 4 camps, since holding them for 15 minutes is a Target, and then march up to Guan Ping's camp. After you take him out you just ride east to the next camp to take out Yue Ying. After that you should take down Wang Ping and his ambush friends to rescue Xiahou Ba. Start killing the remainder, but leave the guys inside the Main Camp. I'm not sure, it might be after 10 minutes, but an ambush force will appear outside all 4 of your camps. Just hop down a few cliffs on your horse and you should get them all starting from left to right in no time. Now you have to wait. Wait for the time to hit 75 minutes left and get the Target for holding the camps before you finish off Liu Bei. He's not very strong, so your guys should be able to fend for themselves.