She told the BBC her husband remains “strong and persistent” in a “tiny room” behind six prison gates, but she worries he could be “harmed”.
“I will not leave Besigye’s food at the gate (as ordered). I will go there and see my husband because I do not trust him even for a day,” said Ms Byanyima.
“Maybe I’ll take a tent and sleep there…if they want,” she added.
Besigye ran for president four times against President Yoweri Museveni, who has been in power since 1986.
But the veteran opposition politician has been less active in politics in recent years and did not participate in the 2021 elections.
However, Besigye returned to the headlines last month after he was dramatically kidnapped while visiting Kenya and forcibly taken to Uganda.
He was then charged along with assistant Obeyd Lutale. He also denies the allegations.
A military court extended Besigye’s detention until January 7, dashing his family’s hopes that he would be home for Christmas.
Ugandan Prisons Service spokesman Frank Bain Mayanja told local media that the seven-day curfew was meant to increase security during the festive season and prevent escapes.
“Christmas is exciting and most prisoners don’t want Christmas inside. They are probably planning how to break out of prison and get out,” Mr Mayanja told NTV Uganda.
Prison services initially announced a ban on visiting the prison for almost a month, but later reduced the ban to seven days.
Ms Byanyima told the BBC she was also concerned about the recent change in management at Luzira prison, questioning why a “young and inexperienced” official had been appointed to run the prison.
“It’s very suspicious and makes me question their intentions,” she said.
“I do not trust his (Besigye) life to those who kidnapped him. I will try to see him as often as possible,” added Ms. Byanyima.
Mr Mayanja said the leadership change was an “administrative matter” and had nothing to do with Besigye.
He added that Mrs Byanyima should trust the authorities to take care of her husband because “we have the means and mechanism to keep him alive”.
“I think she should let us do our job,” Mr Mayanja said.
This is the second time that Besigye, who has clashed with Museveni’s government over the past two decades, has spent Christmas in prison.
In 2005, he was arrested while returning from a political rally on the eve of the 2006 presidential election and charged with treason. The charges were dropped by the courts.
In a separate case, he was also accused of rape. The charges were later dropped. He said the allegations were all part of a campaign of political persecution
In the latest case, Besigye objected to the military court, saying he should be tried in a civilian court if there is any case against him.
Museveni defended the use of military courts to try civilians.
He said any weapons-related crimes are tried by a military court to ensure stability in the country, as civilian courts take too long to hear cases.
Hundreds of civilians have been tried in Uganda’s military courts, even though the Constitutional Court has ruled against the practice.
Opposition parties have often complained about restrictions on political activity, arguing that Museveni is afraid of political competition.
Museveni’s supporters deny the allegations and say he has maintained stability during his nearly 40 years in power.
