Skinner died on March 23 at her ground-level retirement flat in Holtspur, Buckinghamshire. She was 85, reported Us magazine.
"Tracey and her family are deeply saddened by the death of her mother, Doreen," a spokesman for the star said in a statement.
"The family would like to thank everyone for the kind messages they have received and ask that their privacy be respected at this difficult time."
Ullman, 55, reportedly visited the damaged home on Thursday.
"The fire started in the middle of the night and the poor lady died," one neighbour said, adding, "We are all very shocked.