This question and this question go into the details of Squirrel Girl's power stats, which started as a joke in various Marvel books. I'm going to answer from the perspective of the Unbeatable Squirrel Girl series written by Ryan North and illustrated (until very recently) by Erica Henderson.
In this series, it's shown multiple times that Squirrel Girl "defeats" her opponents by talking to them, understanding them, and either befriending them or outsmarting them.
For example this is how she "defeats" Galactus:
She has a similar approach to Kraven:
These are the in-universe explanations of how Squirrel Girl defeats such strong opponents, but a lot of the earlier mentions were more of a joke than anything else.