Best way to express a change of subjects in a succession of events
Actually the second one is quite natural. 

她跟朋友打网球以后，她去吃饭。

This is actually the most legit you can get for this case, otherwise you will have to alter the meaning of your sentence a bit. Like:

她在网球场和朋友约好了， 然后再去吃饭。

Which means, she had a plan to go to tennis with her friends, and then dinner.