What factors must be considered to determine whether a defendant's attorney failed to object at sentencing?

The court relied on both the nature of the crime and the use of a knife to impose the upper term for manslaughter and the one-year term for use of a weapon. Defendant argues neither factor may be relied upon. Defendant concedes her attorney did not object at sentencing, and she acknowledges that an objection is required to preserve these issues on appeal. (People v. Scott (1994) 9 Cal.4th 331, 353.) Consequently, she makes the alternative claim her attorney provided ineffective assistance of counsel by failing to object. We reach the merits of defendant's claims in an effort to determine if there was error, and whether any error caused prejudice.