A semi-colon is used as a way to separate the two independent clauses more than just a comma and coordinating conjunction. A semi-colon has a firmer break in the thoughts. A comma and coordinating conjunction is like a California stop (or a rolling stop) at a stop sign, and the semi-colon is like a full stop but starting up again right away.
2. She didn’t know what to say, she was stunned into silence.
She didn’t know what to say; she was stunned into silence.
Here we use the semi-colon to connect these two sentences. Both actions of the subject are completely connected. Semi-colons also help to keep tension high when in an action scene (though, complete shorter sentences will help more adequately).
8. The full, bright moon rose above the tree line, the light shone down onto the one path that led into the forest.
The full, bright moon rose above the tree line; the light shone down onto the one path that led into the forest.
Using a semi-colon here allows the two sentences to stay closely connected and for the reading of it to be more poetic than a pure stop that a new sentence start would give. This connects more closely the light and the moon.
9. She wanted to go to the party, however, she had no ride.
She wanted to go to the party; however, she had no ride.
Whenever you have “however” in a sentence, there is a great likelihood that a semi-colon will need to be placed on one side or the other of it. It is not, however, always the case (see what I did there =P). The likelihood that it will happen is high. You still have the two independent clauses: “she wanted to go to the part” and “she had no ride” can both stand-alone as sentences.