We get the following diagrams:
S0 --> {S2}
|
S3 --> {S2}
S1 --> {S0;S2;S5}
|
S4 --> {S2;S3;S5}
So, it is clear that S0 is equivalent to S3. Also, S1->S0 is simulated by S4->S3, S1->S2 is simulated by S4->S2, and S1->S5 is simulated by S4->S5. Finally, S4->S2 is simulated by S1->S2, S4->S3 is simulated by S1->S0, and S4->S5 is simulated by S1->S5.
It seems that you ignored that S4 can also move to S5.