Of the 31 absentee ballots that have become the focus of an investigation into possible election fraud in Hialeah, at least one appears to have a forged signature.

The ballot belonged to Zulema Gómez, 81, who entered a nursing home five months ago suffering from Alzheimer’s and a brain tumor. On the ballot’s envelope someone wrote: “The lady is my sister. I sign like this because she has arthritis + she has difficult signing. Thank you.”

However, her sister, Olga Gómez, said Wednesday that she never wrote that message. Two weeks ago, she said, Daisy Cabrera took the blank absentee ballot and promised to go to the nursing home in Miami Springs and deliver it to Zulema. The sisters have known Cabrera for four years, when she visited them during the 2008 presidential election to help them with their absentee ballots.

“She was going to the [nursing] home,” said Gómez, 68. “I don’t know if she actually went, but it’s a lie that I signed that.”

Cabrera could face serious charges if it is established that she forged the signature on the ballot.

Last week, Cabrera, a well-known “ballot woman,” or boletera, in Hialeah, was detained and questioned while carrying a dozen ballots while she rode in a Toyota Camry driven by Matilde Martínez. A day before, she had taken 19 ballots to a post office in Hialeah, not knowing she was being watched by detectives from the Miami-Dade Police Department’s Public Corruption Unit.

She has not been charged with a crime, although a county ordinance prohibits carrying more than two other people’s absentee ballots. The Miami-Dade State Attorney’s Office has said it is expanding the investigation to determine whether a felony has been committed.

On Wednesday, El Nuevo Herald reporters reviewed the envelopes of the 31 absentee ballots that authorities delivered to the Miami-Dade County Elections Department.

The alleged victims are Hispanics whose ages range from 43 to 100 and who live in apartments and houses throughout Hialeah. All but five of those voters are at least 70 years old. A few of them are illiterate. Some said Cabrera filled out their ballots and had pressured them to vote for the candidates of her choice. None of them said they received money in exchange for their ballots.

And some do not remember whom they voted for or whether they had signed their ballots.

“Maybe I did — I don’t really remember,” said Paula Montero, 98, who is illiterate, scratching her head as if in a daze. “But she filled it out. She wrote things there. I don’t know what she wrote on the ballot.”

It has not been determined whether someone paid Cabrera, 56, to help voters with their ballots.

Those who defend her say she is a humble woman who loves politics but might not have known about the ordinance that forbids collecting of others’ ballots.

She is known as a volunteer who was close to Hialeah City Council member Vivian Casals-Muñoz. She has also worked for the campaigns of state Rep. Eddy González, state Sen. René García, and former state Sen. Rudy García, who ran unsuccessfully for Hialeah mayor last year.

González and René García have acknowledged that Cabrera made calls to voters during their campaigns. Former members of Rudy García’s campaign said Cabrera did similar work for him.