I, too, experienced the death of a dear pet as a child. I am sure your daughter is grief-stricken. I am not concerned that Bentley's death still pains her even a year and a half later, but I would be concerned if she is affected negatively in her present ongoing life (e.g., continuing sadness, anxiety, fear, anger) by a continuing focus on his death.
Kids need to grieve over their pets' deaths and move through all the stages of that grieving process. I wonder if this was her first personal confrontation with death. I also wonder if indeed she may have been suppressing an anger toward you and/or has been dealing with the thought that she could have prevented his death by insisting you get him or by getting him herself. Dealing with the "natural" death of her pet has been hard enough; the fact it was preventable makes it even harder to understand. Although she says she doesn't blame you, how could she not see you as the cause of his death, unless, of course, as I suggested, she blames herself as the "owner" responsible for his welfare.
Did Bentley ever have a burial or appropriate ritual to begin the healing and grieving? If not, it's not to late to do something to commemorate his life and use it as a chance to talk about everyone's feelings concerning his life and death. You clearly would not have asked this question unless you felt your daughter was feeling too much pain too often over an event that happened a year and a half ago. Has there been another pet purchase? If not, why not? You should also do a library search for age-appropriate books on kids dealing with the deaths of their pets; there are some superb books available on this subject. If this death continues to affect your daughter's life -- cheating her out of a normal, full range of emotions -- a visit with a good child therapist may be useful and needed.