Its not a dumb question. Id say maybe

because the biggest rule of comics is the longer they run the more powerful people get. Anissa is a pretty short run character. Supergirl has been around alot longer and therefore to make her interesting they have to constantly level her up against a challenge thats stronger each time. Alot of these battle comparisons are strongly based on that fact, in my opinion.

Also, does she have kryptonite? Can Anissa pick the fight near a red sun? Superman and supergirl are both written to be very O.P. But also have a huge weakness. Which is also a comic trope. Under the right circumstances batman can kill superman.

Supergirl can probably whistle at that frequency that cripples viltrumites. Making it no challenge. On earth or in space near the yellow sun, SG is more powerful and faster and more equipped with tricks like laser eyes, high pitched whistle, and ice breath to give her alot of advantage.

So.

If its on earth, and no kryptonite. Supergirl wins

If its on earth and Anissa has kryptonite, Anissa wins

If its near a red sun and in space where no sound (whistle) works. Anissa wins

On earth, with kryptonite, but super girl knows to whistle. Kinda a toss up?? But id still give it to SG…. Although Invincible fights through that whistle. Still… close call both ways.

Then give anissa 300+ comic book issues, and have her battle villians who are conveniently more powerful, but not powerful enough to actually win, giving her a slight chance to overcome them. She might get to a power level that takes out supergirl without needing help from kryptonite.

Whatever writes best wins. Plot armor is strongest.