The real of goal of her quest is neither to win the race nor aid her in pursuing vengeance but rather to help her come to terms with her loss so she can reach her final stage of grief.
Was it wrong for her to not be upfront about her true intentions? From an ethical point of view, yes. However, intense grief over the loss of a loved one can cause people to think and act irrationally like we see in Claire’s quest. It’s too easy to blame someone for possibly playing a role in the death of someone you love and even wish violence upon them as if that will somehow bring them back. (I’m speaking from experience).
Winning the race is not the best outcome. Claire is unable to move on from her current stage of grief since she was never able to directly confront the man she believes responsible for her husband’s death.
Letting her kill Sampson is also not the answer. After killing him, she will be filled with regret and be left with a feeling of emptiness as killing Sampson did nothing to bring her husband back. Her pursuit of vengeance was entirely in vain.
The best outcome is helping Claire directly confront the man she believes is entirely responsible for her husband’s death but instead of letting her pull the trigger you tell her the cold hard truth. Despite the risks, her husband knowingly chose to participate in a deadly race that ultimately cost him his life. After coming to terms with this, she’s finally able to reach her last stage of grief.
Unfortunately, most players don’t know of this outcome as it’s slightly hidden behind specific dialogue choices before the last race (tell her you’re out and then tell her you’re in but only to finish the race).