<human>: Can you provide a brief rundown of the text in within 3 sentences?

She's been very good with other dogs. She plays very well, doesn't snarl or tackle, or any other rough play. That is, until 2 weeks ago when a white shepherd mix named Pearl came to the dog park. Immediately, Pearl saw Opal as a worthy opponent and started wrestling with her. Pearl's play-style seemed to be pretty hardcore; snarling, growling, basically play fighting. I didn't like this at all and I wanted to break it up and take Opal home, but Pearl's owner said they were having fun and it was fine. So I stayed and they really did have fun. They wrestled for 10 minutes at a time, then took a water break, wrestled, then leaned on us for a minute, wrestled, etc. Eventually they were both sufficiently exhausted so we went home.      
So we went back to the dog park today and everything was normal. Opal was friendly as can be, running and chasing other dogs, no growling to be seen. But then after about 20 minutes of playing nice with all the shelties, cattle dogs, and labs, a white shepherd mix came. As soon as Opal saw him through the fence, she ran up (tail wagging) and growled. I called her to me so that he could come in without getting overwhelmed, but when the other dogs ran up to the gate, she went with them, and tackled him when he came in. I called her over to me and made her stand by me while he got a little more settled, but I actually had to hold her collar to keep her from chasing him. As soon as I let her go, she tackled him again. (this is all with a wagging tail but with some nasty-sounding growls.) The white dog was definitely not into it, so I decided we needed to leave.
<bot>: A white dog picked a play-fight with my normally docile dog, and now she seems to think all white dogs want to play-fight.