The answer was Monday.
The Cardinals hired Jen Welter as an assistant coaching intern for training camp and the preseason to work with inside linebackers. She is believed to be the first female coach of any kind in the NFL.
"Someone asked me yesterday, 'When are we going to have female coaches?'" Arians said. "The minute they can prove they can make a player better, they'll be hired."
Welter took to Twitter after the announcement.
Welter, 37, has been making history throughout her career. In February, she became the first female coach in a men's professional football league when she was hired by the Texas Revolution of the Champions Indoor Football league to coach linebackers and special teams. The Revolution's general manager is Hall of Fame wide receiver Tim Brown. In February 2014, she became the first female to play a non-kicking position in a men's professional football league when she played running back and special teams for the Revolution.
Welter played professional football for more than 14 years as a linebacker, mostly with the Dallas Diamonds of the Women's Football Alliance. She helped lead them to four championships.
She will join linebackers coaches Bob Sanders, Larry Foote and recently hired Levon Kirkland.
A news conference is scheduled for Tuesday.
Speaking to azcardinals.com on Monday, Arians said: "Coaching is nothing more than teaching. One thing I have learned from players is 'How are you going to make me better? If you can make me better, I don't care if you're the Green Hornet, I'll listen.'"
"I really believe she'll have a great opportunity with this internship through training camp to open some doors for her,'' Arians said.
It's the second such barrier to be broken in the NFL this year. The league announced in April that Sarah Thomas would be the first woman to be a full-time NFL official.
Vice President Joe Biden tweeted his congratulations to Welter on Tuesday:
Information from The Associated Press contributed to this report.
Jen Welter hired by Cardinals
ESPN Cardinals reporter Josh Weinfuss breaks down why Arizona decided to hire Jen Welter, believed to be the first female coach in the NFL, as an assistant coaching intern for training camp and the preseason to work with inside linebackers.
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