Cow Having Hard Time with Hot Weather

We have a 3 year old cow that is really struggling with the 90 degree, high humidity, southern Indiana heat.  She stands in the coolest place she can find, usually in some water, and pants with her tongue out just trying to get all the air in she can.  She's not overly fat, small in size, and we body clipped her in May to help her.  But as it's got hotter she's still not taking it well.  The odd thing is, she has a late March steer on her that does the same thing.  He's a small calf, low birthweight, follows her body size, and is not overly haired up, but he's the only one of the calves that is bothered by the heat.  Is there a chance this is an inherited trait?  Thinking of culling her if it is.  Concerned one day she'll collapse from heat exhaustion and if her offspring are all like this, we're just promoting the problem.  The calf has 2 other sire mates and they are fine.

I just culled a cow with similar symptoms.
She had three steers that did not show symptoms.
Two heifers have shown them.
I thought I might find her dead at times, but she
always raised the heaviest calf and bred right back.
Finally culled her due to a nerve injury.

Are you on fescue pasture? 
Early on, she had trouble with fescue.

Good luck.

Better question, is she a TH carrier?

Yes, we have fescue mix, but this started back in April, early May, before the fescue got mature and the cool season grass was plentiful and lush.  And it was comfortable weather.  She is a Man Among Boys, so I'm guessing THC.

Vigor and adaptability are absolutely hereditary. If she's breeding back and weaning respectable calves, I see no reason to even address the issue. If it affects her to the point she fails to breed back, cull her.

I have one black Walks Alone cow that is suffering through our 100 degree plus heat.  She is coming with her 3rd calf.  She has that thick hair coat of a TH carrier.  I am going to clip her, even though her hair is not that long, and see if that helps.  All my other cows, including several Walks Alone cows, handle the heat just fine.  I do have plenty of shade for them in all my pastures.