As a joint account it will show on both CR. I do not know how each lender will handle it.Your score might not mean anything to them as she is in good standing.
I would think it would help your score but I do not know by how much.
I just applied for 5 new cards for DH & wow did it help him. he was at 85 UTI now I think he is below 30% but his score was EQ 688
They will take her CL + her UTI and add it to you also.You will not get here scores. But it might help you get your up.