She set about getting Ms. González to New York. She asked a few mothers she had just met at a donation drive for separated children — and then the public — to help post Ms. González’s $7,500 bond.

[Yeni González was the first woman to have her bond paid by the New York women. Follow her cross-country journey to be reunited with her children.]

Like the Texas-based nonprofit Refugee and Immigrant Center for Education and Legal Services, or RAICES, which raised more than $20 million after launching a Facebook fund-raiser to cover one detained parent’s $1,500 bond, the New York group soon exceeded its once modest goal. As of this week, Ms. Schwietert Collazo’s group, which has gone from being called the Yeni González Support Team, to Immigrant Families Together, has raised more than $300,000. They call themselves “a network of Americans committed to rapid response unification of families separated by the ‘zero tolerance’ policy.”

Sara Farrington, a playwright, joined the group and “blitzed mom groups within 100 miles of here” on Facebook to raise money. “People ask me, ‘Why this?’ ‘Why aren’t you focusing on the midterms?’ I think it comes back to empathy,” she said. “To the gut punch of a mom separated from her 5-year-old. The reason that this has exploded, I truly think, is that moms have put themselves in that situation. It has hit a primitive motherly nerve. I think it all stems from, ‘What if it were me?’”