Sally Ann John, who disappeared from Swindon, aged 23, in 1995, had been working as a prostitute.
On Thursday police arrested three men in their 50s on suspicion of her murder.
"Every day is difficult without Sally Ann and I appreciate the understanding I have been shown," said Lesley John.
In a statement released through Wiltshire Police, she said: "The police have been keeping me informed of progress with the investigation into Sally Ann's disappearance and the arrests yesterday give me hope.
"I feel it is important that the police are able to continue to investigate without speculation from anyone and I hope that the community will support me in this."
The trio, including two men from Swindon aged 50 and 52, and a 52-year-old from Chippenham, are still being held on suspicion of kidnap and murder.
Sally Ann's disappearance was initially classified as a missing person but police launched a murder investigation in 2014.
She was last seen on Aylesbury Street on the morning of Friday 8 September 1995. Her body has never been found.
The mother of a woman who went missing 20 years ago and is believed to have been murdered has said the recent arrests have given her hope.