Volunteers working with Catholic Charities frequently went across the border to Matamoros, where the families are camping out, and bring them hygiene items, food, and anything else that they need. There are estimated to be about 650 migrants in the camps currently, down from several thousand at its peak.
The coronavirus pandemic has made helping families along the border even more difficult. In March, President Donald Trump shut down nonessential travel across the US-Mexico border, and indefinitely suspended the asylum system.
In Matamoros, Pimentel says she often would encounter entire families waiting at the border, fleeing persecution in their home countries, who have nothing to eat except what is brought to them by aid groups. Matamoros is one of the world's most dangerous cities, with frequent kidnappings and murders.
"I really touches my heart to hear that, and to see the children and families hurting so much. It really hurts to see children in such poor conditions," Pimentel said.
In addition to basic supplies, Catholic Charities was helping to provide legal assistance, workshops, and explanations to the migrants, who often have little idea how the US immigration system works, and have no idea how their hearing will go. Often there is not even a translation available for migrants who do not speak English, she said.
The United Nations refugee agency says in 2019, there were about 70,000 who filed for asylum in the US from Mexico, up from 2,000 in 2014.
Pimentel wrote a July 2020 op-ed in the Washington Post, warning that squalid conditions at the Matamoros camp and a lack of water and sanitary supplies made the camp "a potential outbreak waiting to happen."
To Pimentel, helping the destitute migrants in the area is part and parcel of the charity that the Catholic faith demands of every believer.
"If we believe in a God of love, a God who tells us that we must welcome the stranger, feed the hungry, clothe the naked- Jesus was very specific in saying 'Look for me and you will find me in them, in those people who are hurting and suffering,'" she said.
"How else do we want to receive Jesus if he is telling us already: 'This is where you will find me.' And so if we don't do that, I think we are failing to understand Jesus in our lives, and what He is calling us to do."
The Catholic bishop of Brownsville praised Sister Pimentel's work Sept. 22 and congratulated her on her distinction.
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"Thank you, Sister. You help us all come together in the Valley to face our challenges,
you help us learn how to help each other, how to protect the vulnerable, to not lose hope...and to be a sign of Christ in the world," Bishop Daniel Flores of Browsville said Sept. 22.
President Trump visited McAllen during January 2019 in an effort to drum up support for $5.7 billion in funding for a wall along the border with Mexico. Pimentel said after the visit that she was "truly disappointed" that she did not get a chance to speak during a roundtable discussion with the president.
Pimentel said at the time that if she had had the opportunity to speak, she would have emphasized that she understands the importance of border security and keeping the country safe, and that the Border Patrol - with whom she says she has always had a good relationship, and prays for daily - should be supported.
"We also must recognize that there are a lot of families, innocent victims of violence, that are suffering," she said.
"And we find them here in our community, and we as a community are so generous in responding to help them, to be there for them. It's a part of who we are as Americans, very compassionate. And that is a side that unfortunately our president was not open to listening to."