Suzanne Clark Simpson‘s sister had a bad feeling when she first learned the Texas mother of four was missing.

“It’s inconceivable,” Teresa Clark tells PEOPLE. “I knew she wasn’t alive. Suzanne does not disappear.

Suzanne, a real estate agent from San Antonio, was last seen when she, her husband and their youngest child attended a birthday party on October 6.

At the time, Clark was in a hotel in Hong Kong when she received a message from one of Suzanne’s college-aged children asking if she had spoken to her sister. No one had heard from Suzanne since 4 p.m.

“I immediately knew my sister was gone,” Clark says.

Then she learned that her sister had missed a hair appointment.

“The first red flag was when she missed her hair appointment: no one misses a hair appointment,” Clark says.

Then her sister didn’t pick up her youngest child from kindergarten.

“That was the second red flag that there was nothing normal about this,” Clark says.

Suzanne was officially reported missing on October 7. After her disappearance, her husband of 22 years, Brad Chandler Simpson, was charged with assault causing bodily injury to a family member and unlawful restraint.

Want to stay up to date with the latest crime coverage? Register for PEOPLEThe free True Crime newsletter for breaking crime news, coverage of ongoing trials and details of intriguing unsolved cases.

During a press conference on October 9 broadcast by KENSOlmos Park Police Chief Fidel Villegas said Brad was arrested after failing to show up for a meeting with police. Villegas said that after learning of Suzanne’s disappearance, police became aware of an altercation at the family home that may have turned physical.

On Monday, November 4, Brad’s defense attorney, Steven Gilmore, told PEOPLE, “I have no additional comment at this time.”

On Thursday, November 7, Brad was accused of murderaccording to the Texas Department of Public Safety. The Olmos Park Police Department will hold a press conference at 2 p.m. on Friday, November 8.

Gilmore did not respond to PEOPLE’s request after the new accusations.

Clark tells PEOPLE that as far as she knows, her sister’s body has not yet been found — but she believes her sister is no longer alive: “There’s no hope,” she says.

The authorities nevertheless continue their search.

“They’ll find her,” Clark said. “She was a great mother, a great daughter and a great wife. She was loved. We will do everything we can to bring her home.

If you are a victim of domestic violence, call the National Domestic Violence Hotline at 1-800-799-7233 or go to thehotline.org. All calls are free and confidential. The hotline is available 24/7 in more than 170 languages.