Kelly Clarkson is defending herself as a working mom after a social media user said her marriage "didn't work" because of her busy schedule.

When a Twitter troll said "no wonder her marriage didn't work" in response to Clarkson's filling in for Simon Cowell as a judge on America's Got Talent this week, Clarkson responded to the user, urging them to "aim higher."

"Wow," Clarkson, 38, wrote on Twitter. "Shaming a woman who has a great work ethic, is a great mom, and who steps up and fills in when a friends asks for a favor because that’s actually what 'good old country girls' do.... this can’t be who you are deep down."

"I have more faith in your heart," she added. "Aim higher please."

Clarkson is mom to daughter River Rose, 6, and son Remington "Remy" Alexander, 4, both of whom she shares with Brandon Blackstock. The "Since U Been Gone" singer filed for divorce from Blackstock in June after nearly seven years of marriage.

The American Idol alum acted as a guest judge this week on AGT while Cowell, 60, continued his recovery from back surgery after falling off an electic bicycle over the weekend.

A source told PEOPLE on Monday that the executive producer was in "good spirits" and "walking around again as much as he can."

On Tuesday, Clarkson joked about emulating Cowell's tough reputation in an Instagram video, saying that she would be bringing "country" to the show instead because she has the "worst British accent in the universe."

"It's almost showtime y'all! Getting ready to take over for @SimonCowell! I really need to work on my British accent... 😂😂" she wrote alongside the video. "Looking forward to watching all of the acts!"

In June, Clarkson opened up about the challenges of motherhood, acknowledging that while "overwhelming" at times, there is "no greater gift."

"You are going to be inspired to do all of these magical things with your kids. Do things you've never done before. Try things you've never done before," she said during a virtual ShowHER Love baby shower for new and expectant moms as she teamed up with Carter's. "It is such an awesome experience being a parent. I know it can be overwhelming, but it is so amazing. You aren't just molding their little lives -- it's changing you in the process, too."