Katharine McPhee's Stepdaughters Erin and Sara Foster Defend Post-Baby Bikini Photo: 'Let Her Live'

Katharine McPhee's family is coming to her defense.

On Tuesday, the 37-year-old Smash star's husband David Foster shared a photo of the mom of one on Instagram, showing her posing in a black bikini. "What baby!" Foster, 72, captioned the post, presumably referencing his wife's post-baby figure after she gave birth to their son Rennie David earlier this year.

After some social media users criticized his comment on the photo, McPhee responded on Wednesday in a post of her own.

"I'm sorry but we are not sorry. And for all of you who can't deal with it maybe this helps. I've struggled with weight my whole 20s and 30. I've gone up and down 10 times over. Does that make you feel better? There is nothing wrong with that — most people do," she began in the caption alongside another photo of her in a bathing suit.

In the comment section, Foster's daughters Erin, 39, and Sara, 40, showed support for McPhee's message.

"If I can accept my step mom looking like this, you certainly should be able to," joked Erin. "The photo wasn't altered or filtered and she's had no surgery. You can't shame someone for feeling cute after a baby whether she's sharing stretch marks or a six pack. Let her live."

Added Sara, "If you had had cellulite and stretch marks in the photo and the caption was exactly the same we would all be celebrating his post. But you don't and that's not allowed to be celebrated."

"Also, you had a baby almost a year ago, not yesterday," she continued. "You have been working your ass off in the gym. Let's complain about women and husbands who post 3 week postpartum pics with their full body lipo, filters and altering apps that make us all feel like shit. People are crazy."

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In her caption, McPhee continued, "I lost this baby weight without dieting. Zero. Diets are the worst and I've had zero pressure from anyone. I've let me body do its thing and found a great workout. That's it. And guess what? I'll probably gain weight again at some point too. Who cares? BUT people freaking out about what my husband captioned seriously get a life... Stop being so offended by what people post who have zero impact on your life and move on."

"Maybe you should have more of an attitude of like, let's say… 'oh that's nice he thinks his wife is hot,' " she concluded. "I cannot with this overly sensitive society right now. But as Taylor Swift said haters gonna hate byyeeee."

McPhee and Foster welcomed Rennie in February after tying the knot in June 2019.

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The actress said in March that her "biggest challenge" while carrying Rennie was the fear that her past struggles with disordered eating and bulimia would return as her shape grew. That gave McPhee a "healthy love-hate relationship with pregnancy," she told E! News.

"I think that I struggled a little bit with the getting bigger part," she said.

After Rennie's birth, though, McPhee found that her mindset completely flipped. "What I didn't expect was to have the baby and then be so at peace with my body," she said. "I had this, wow, like this huge appreciation of what my body had just done and given me that I wish that I'd given myself a little bit more of that grace through the pregnancy."

In the months since, McPhee said she hasn't had any desire to push herself to lose weight.

"I actually had this huge gift where I felt zero pressure to kind of get back to a certain standard," she said. "I was just like, 'Wow, this is such a moment in time to enjoy a new baby and give thanks to this incredible body that just did something so spectacular, like truly a miracle.'"

"I'm so much happier, so much more peaceful," she continued. "And actually, the extra weight that I gained while I was pregnant has just sort of fallen off naturally. I never had to torture myself to do any of those things."