You know, this is an interesting match, because it's one of those cases where appearances end up being rather deceiving.
First, let's hammer down the stats. Frost downscales from
0.09 for being considerably weaker than Scorpion but not enough to not be a threat, while Karin solidly scales to
0.1; an almost negligible difference, but it's still something.
About LS, Frost as of now scales to
1200/1500 kg, while Karin to baseline Class 5. Once again, small difference but in Frost's favor.
Now, onto the actual analysis.
While Frost does have a better arsenal, she suffers from some major problems. First, as a villain in the Netherrealm continuity, she is legally forbidden for winning against anyone. In all her appearances, whether she was a human or a cyborg, she always got her ass handed over, namely Scorpion, Sub-Zero, Raiden and Nightwolf. In her not-canon-anymore comics appearance she also gets submitted by an unarmed Cassie in just a few moves the moment she decides to fight seriously.
MKX and 11 also portray her as naive, rash, delusioned, stubborn and overall unworthy, which is why she got cast out of the Lin Kuei in the first place, preventing her from completing her training and making her rely on her cybernetic enhancements.
On the other hand, Karin already has a good streak of victories, draws, compliments etc... in relation to many figthers. Her instruction alone is better than Frost's, as she has a clear record which includes a bonkers amount of accomplishments in the japanese martial system, the creation of her own fighting style that mixes several existing ones and the secret style of her family. She is also used at going toe to toe with characters that are stronger than her, either in LS (like Zangief) or AP (to the level of M. Bison, with whom she just exchanged fists [not allowing scaling], but it regarded by the
narrative as quite the feat).
I also must say that Karin consistently fights people with better arsenals than her and is especially used at fighting ninjas, from those that serve under her, to the likes of Ibuki and Zeku, both having much better acrobatics than Frost, strictly speaking in regards to ninja shenanigans.
Lastly, I must point out her higher stamina (while Frost has little to not feats, and has been knocked unconscious by brute force more than one time) and has at least one safe way to counter ranged attacks.
All of this not to say that Frost is a pushover (even though Netherrealm trest her as such), but her writing, characterization and narrative brings her down to such a level I feel confident in saying Karin would beat her despite the more notable advantages.
Frost can surely score a victory and a murder quite many times, just not enough to surpass Karin's own chances to bring home the victory, imho.
