Heidi Broussard, the Austin, Texas, mom found strangled to death one week after she vanished, had been friends for years with Magen Fieramusca, who police believe is involved in her disappearance.
"You were supposed to be Heidi's friend," Broussard's friend, Rachel West, told "Good Morning America." "I hope she rots."
Broussard, 33, and her infant daughter had been missing since Dec. 12 when Broussard was discovered strangled to death in a home near Houston on Dec. 19, according to officials.
An infant girl was found alive and healthy at the scene, and police say DNA testing is underway to confirm that she is Broussard's baby, Margot.
Broussard's friend, 33-year-old Fieramusca, was charged with kidnapping.
According to an official briefed on the probe, police are investigating whether this alleged kidnapping was part of a plot for Fieramusca to take Margot as her own child.
Investigators are aware that Fieramusca had allegedly been acting like she was pregnant and telling people that she was expecting a child, the official said. Authorities are now trying to determine whether she was, in fact, pregnant, the official told ABC News.
Baby registries allegedly connected to the suspect were found online, the official said.
West said she only met Fieramusca once, in May -- "probably a month after Heidi found out she was pregnant."
But Fieramusca and Broussard had been friends for "probably 15 years, plus," said West.
West said she spoke to Fieramusca "the whole week" Broussard was missing -- and never suspected Fieramusca may be involved.
West said her friend's "horrific" death has left her feeling "complete anger."
Broussard was adventurous, passionate and an "amazing mother" to baby Margot and her 6-year-old son Silas, said West.
Now her son has "just lost his whole world," West said.
Fieramusca was booked at the Travis County Jail Friday night on two charges of kidnapping and one charge of tampering with evidence with intent to impair a human corpse.
Additional charges are possible, police said Friday.
ABC News' Kaylee Hartung, Josh Margolin and Kieran Mcgirl contributed to this report.