Separating her from Kara doesn't seem too difficult. They're different ages, don't really look or (usually) act the same, go by (admittedly only slightly) different names (Kara and Karen), etc. Kara is written as either a teen or someone in their very, very early 20's while Karen is closer to Clark's age and is already well established in her career. Making these two distinct from each other doesn't seem any harder than making Dick Grayson and Jason Todd distinct.
Though I've also suggested switching Karen's powers around. She's from another universe, who's to say that the yellow sun on main earth affects her the way earth 2's sun did? I'd love to see her have ice vision and fire breath, just to help play up the fact that Karen's a different breed of Kryptonian.....but that makes her too much like Bizarro, regretfully, and changing her power set too much takes away what little "Super-connections" she gets to have.
No, I understood what you were saying man. That's why I said In my opinion, the only characters who absolutely have to be at the top of their fields are the A-list characters you want at the top of the company line (and even that can be non-tangibles like "best Everyman" or "best anti-hero"). The B- and C-list heroes *can* be the best in their fields, and several are (like Magnus, Palmer, Stein, etc) but if they're just "working class" heroes that's fine too. I love Power Girl and I want the character to be successful, but as long as she gets quality use I'm fine with her not being the greatest hero at any particular thing. She's still incredibly capable, powerful, and resourceful as is.
But if you want Karen to be the best in her field, then you could always double down on the business stuff and carve a unique spot out for her in DC's corporate landscape. If you run with the idea of Karen investing in the Power Company, right there you've got the chance to make Karen the Queen of For-Hire Heroes. Or you could have Starrware (or whatever her company is called) be the world's leading company in space travel technology. Sort of make Karen the DCU's Elon Musk.
Or you could lean into her "black sheep of the Super-family" thing. Which, ironically, would probably make her more involved with Clark and his clan, since you'd have to include Karen in their get-togethers to highlight how she's the black sheep.
If Jason Todd can build a niche out of being the resident d-bag in the Batcave, Karen can make a similar "outsider" role for herself work. But this is more "theme" than "in-universe area of expertise."