A source tells ET that "Britney has had another very difficult week" and adds that "getting through each day is a challenge."
"Performing again right now or anytime soon is not an option," the source says. "She is in no state to be able to take care of herself let alone to do live shows. She needs to get the right combination of medication and therapy for more than just a 30-day stay in a facility for her to be able to function properly."
The source says that Spears "loves to perform" and it "would be devastating" if she didn't have the opportunity to take the stage again.
"[Britney's manager] Larry [Rudolph] stating she might never be able to perform again will hopefully be eye-opening to her," the source says. "He didn’t say it to hurt her but she does need to realize how serious her situation is at this time. She has a very good support system but she is adamant about doing things her own way."
The source was referring to Rudolph's recent comments to TMZ where he stated, "From what I have gathered, it's clear to me she should not be going back to do this Vegas residency, not in the near future and possibly never again."
"We had to pull her show because her meds stopped working and she was distraught over her dad's illness," Rudolph said of Spears' currently on-hold residency, Britney: Domination. "Last summer, when she wanted to tour, she called me every day. She was excited. She hasn't called me in months. Crickets. She clearly doesn't want to perform now."
"I don't want her to work again 'till she's ready, physically, mentally and passionately. If that time never comes again, it will never come again," Rudolph told ET. "I am only here for her when she wants to work. And, if she ever does want to work again, I'm here to tell her if it's a good idea or a bad idea."
While ET's source says Spears' team "continues to encourage her to get long-term help," Spears "has to want that and so far she seems to be more focused on having the ability to make her own decisions. Her focus at the moment is having her autonomy."
"Functioning without medication isn’t an option for her," the source adds. "Her family has been incredibly worried about her and spends as much time as possible with her."
The source adds that Spears' two sons, Sean, 13, and Jayden, 12, are spending most of their time with their father, Kevin Federline.
"Britney’s boys are well taken care of and live for the most part with Kevin," the source says. "They visit and stay with their mom whenever possible. She would love to have them full time but right now those closest to her feel she needs to leave the custody situation as is until she is back on track."
According to court documents obtained by ET on Wednesday, the judge for the singer's conservatorship case has ordered that there be a Court Investigator's Report at the next hearing on Sept. 18.
Typically, a court investigator researches, examines and interviews all parties in the case and then presents a report to the judge in order to help the courts make the best possible decision. Britney's father, Jamie Spears, has been her conservator since 2008, and became her sole conservator this year after his former co-conservator, attorney Andrew Wallet, resigned in March.
Spears' mother, Lynne Spears, who has not previously played any role in her eldest daughter's conservatorship, also requested special notice of all matters relating to Britney's conservatorship.
ET learned in early April that Spears had checked herself into a health facility to deal with the tremendous stress she's been having over her father's current health crisis. The check-in came just a few weeks after she put her career on an indefinite hiatus, postponing her album in addition to the Vegas residency.
"I am dedicating my focus and energy to care for my family," she said in a statement at the time. "We have a very special relationship and I want to be with my family at this time just like they have always been there for me."
Not long after fans learned that Spears had been checked into a health facility, rumors began swirling that she was being held against her will and a hashtag, #FreeBritney, quickly went viral.