'We’re just trying to get through these few days, we’re anxious, but hopeful,' Jo Jo’s sister Kathleen Bergin has said.
Deirdre disappeared near her home in Newbridge, Co. Kildare, on July 28, 1998.
Jo Jo who was born in Callan, Co Kilkenny, was 21 years old when she went missing in nearby Moone on November 9, 1995.
A major operation now taking place close to Usk Little near the county border with Wicklow is hoping to recover crucial evidence related to the missing women.
Jo Jo’s sister Kathleen Bergin said their thoughts and prayers are with Deidre’s family as they hope they will find her.
“We’re just trying to get through these few days, we’re anxious, but hopeful” she told KCLR Live.
“I suppose there's not a day that goes by that Jo is not in our thoughts.
"The sense of loss has been very hard to come to terms with. It has had a huge effect on her family and her friends and has caused a lot of pain and suffering over the years.
"It’s hard to believe she’ll be gone 26 years next November, but we have to hang onto hope,” she added.
“We always try and hang on to that hope that someday we will find her.
"You often hear about other cases, say after 20 or 30 years or more and the next thing somebody comes forward with a little piece of information and they have their answers, they find their loved ones and the case is solved.
"So that little bit of hope is there.”
Inspector John Fitzgerald, of Kildare Garda Station, told a press briefing this week that there was unusual activity noticed in the wood, a short distance from Usk Little on the evening Deirdre Jacob was last seen.
He said that while the search was related to Ms Jacob’s disappearance, they will "bear in mind" that Jo Jo Dullard was last seen a short distance away.
Ms Bergin said they had been informed that the search was going ahead and that it was based on information relating to Deirdre’s case.
“It’s very close (to where Jo Jo was last seen).
"Our thoughts and our prayers are with Deidre’s family and her friends because God love them, this is such a difficult time for them and please God they will find Deirdre and have answers.
“It just might help another case and we might be lucky.
"They might find something that belonged to Jo as well. We won't know until the search is over, but we have to be careful.
“We can't say that the same person is involved, we don't know that until the day we find Jo Jo. We cannot say that the cases are connected.
“But because of how close it is to Moone, it’s only natural to have hopes.
"Our fingers are crossed and we’re praying that we might just be lucky because if they find Deirdre, and I'm praying that they do, they may get answers and it will give another family hope.”
Ms Bergin appealed for anyone with information, no matter how small, to come forward, and not to be afraid.
“Somebody definitely has information,” she said. “And for whatever reason they couldn't come forward all those years ago, we can only imagine that they must have been under severe pressure and may be fearful of their lives and were told not to say anything.
“But we're hoping that their circumstances have changed and maybe they're feeling that (after) 26 years, if their circumstances have changed, how can they come forward at this stage.
“It's so important for them to know that that's all we want, for someone to come forward and that they will not be judged. This will be dealt with in a very sensitive manner.
“All we want is for them to come forward now and not to be afraid. We are praying that they will find the strength and the courage to come forward..
"Somebody holds a piece of information and no matter how small it is, it could be just what we're looking for, and it could put all the pieces together.
“It would mean the world to us, and we would ask them, please, don't be afraid, take that step and come forward and help us.”