The problem is it legitimizes the president, and she indirectly condones his actions, and creates an alternative narrative, very close to what Republican leaders say, "Oh, well I don't support everything he does, but look at the tax bill". She goes up there, and smiles for the camera, he signs a bill, they do the promo, and people can say "See, he's not racist.....did you see Kim Kardashian's project"
Not to mention, these women have millions of followers and admirers, who are similar to Trump devotees, in that, they simply pledge their blind allegiance. You can create new Trump supporters, or encourage those who were on the fence, or ambivalent, by pushing the narrative that this kind of action creates.
Get the man out of jail. Just don't do it like this.