Because she got caught up in helping to make the hotel run and its antics. Plus, in the two part episode when Dorothy visits, Dorothy admits not having a lot of contact with her friends because she and Lucas needed some time to themselves.
Now off camera, Sophia could have very well went to visit Dorothy. Blanche (Between GG and GP) was off screen visiting her brother Tad in Chattanooga, TN and it was later revealed in a Valentine's Day episode on "The Golden Palace". Anything is possible.