There are two older daughters on the 1901 census, if I am looking at the right folks!
Ida's birth reg will give the name of who is claiming to be the mother.... it is just blank on the GRO index to indicate an unmarried Smart is mom. Her first name should still be on it.
If you don't want to get her birth registration, as a work-around, make a new daughter for Mr. and Mrs. Smart, name her "one of the daughters" or something similar, and attach Ida to her. If you ever figure out which daughter is mom, you can move Ida to her, and delete the fake daughter. At least this way, you get Ida attached.