Five easy ways in my opinion on how Marvel can introduce Squirrel Girl in the MCU.

5) A One-Shot

If the one-shots are still alive at Marvel (sad that we didn't get any this year) it will be a great option for them to introduce her (or prodably her origins) in a 12-minutes one-shot.

4) Guardians of the Galaxy 2

Remember the Howard the Duck cameo in GotG? He was already existing as a character in the MCU, without an origins story. And the fact that Marvel can't use the "mutant" word, it's a great way to introduce Squirrel Girl in a howard-the-duck type of character.

3) Netflix

We have the Netflix series coming soon. There was a period of time in the comics where Squirrel Girl was the babysitter for Jessica Jones and Luke Cage's child. They can introduce her in some of the 5 tv series. I can see her being best friends with Jessica Jones.

2) Avengers: Infinity War Part II

Thanos has the gauntlet and he's the most powerfull being in the universe. Who will be brave enough to stop him once and for all? Squirrel Girl of course. Marvel can make that easy. You have Tony Stark/Bruce Banner/Hank Pym ... What if they were making an organic weapon to defeat Thanos? Wooala, you have Squirrel Girl.

1) A franchise

Or Marvel could just risk it, and say .. "Hey, let's make her a movie!". Who knows, she can even be the next Tony Stark/RDJ, no?