I’m afraid you will not be able to travel without her - you will not be allowed to enter the UK unless she is entering at the same time or is already there.
A quick follow up on this. She joined me, and we had a very smooth entry. However, we did happen to ask the immigration official stamping my visa if she had to be present for this, and he said no, that the approved visa is all that was required, as it demonstrates meeting the requirements. I'll leave open the possibility that there was a misunderstanding on my part or his, but thought I should report back. We're very happy to have that stamp, regardless!