I'd mostly agree with Evelyn's answer, except I wouldn't exactly call it a case of double negation. Here the full sentence would be "it is nothing that chewing a few Nurofen won't fix". If there were double negation, then you might instead say "it is something ["anything" sounds weird here] that chewing a few Nurofen won't fix", but that would give it the opposite meaning. A different example with confusingly similar wording could be "it won't fix anything" vs "it won't fix nothing". This is an example of the double negative, and any person with a solid understanding of English is going to understand the two sentences to mean the exact same thing. I'm not saying you should use the double negative yourself, but grammar purists might imagine the English language differently than how it's actually sometimes used. The structure is a little unusual, but there's nothing really wrong with it. In fact, it's a bit of a fixed expression itself: "nothing ___ won't fix", where you can fill in the blank with whatever you want.

The sentence means that she is in pain, but doesn't want to admit it or complain about it. She's downplaying the fact that she is in pain by making a joke about it. It is a double negative. "Nothing that chewing a few Nurofen won't fix," means "Something that chewing a few Nurofen will fix." (Nurofen is a pain medication.) When she says "chewing," that's part of the joke. When she actually takes the pain medication, she will swallow it with water, just like everyone does. Does that help?

This is referencing actually eating or chewing on a pain reliever medication. The word “Nurofen” is a common pain reliever pill...and yes, the double negative “Nothing and won’t” are being used to add to the mood of the sentence. The mood is lazy and slightly ironic by the writer. Hope that makes sense... Best wishes to you. :)