To make sure she had correctly identified the twins apart. Which was the reason why she had gone in the first place.
Her desire to return was not related to identifying the twins. What she said was, "Whilst I was there I felt I should touch the bodies to see if they could give me guidance on what I should do but I could not summon up the courage to do it. I left and once outside made up my mind to go back and seek guidance from the bodies. However I thought that if I requested to see the bodies again someone may have started asking questions which I could not answer.”
Mugford - 10 September 1985
So, allegedly, she thought the bodies might tell her something, which seems odd if she was so convinced that Jeremy had carried out the killings, or paid a hit man to do so. Essentially, just more lies from Mugford.