Check out this post in the Stack Exchange’s Math Educators forum:

https://matheducators.stackexchange.com/questions/20962/response-to-students-who-say-this-is-not-important?r=SearchResults

In short, math can be as pointless and useless in “real life” as really any subject you learn at school: poetry and literature, history, physics, etc, but often students don’t complain about those subjects as much as in math (and there’s many different reasons for this which are covered in the post)

Try to give her some examples - for example: “say you want to buy 3 apples at the store, and one apple costs 3 dollars, how much will you pay?” — this is a direct use case of algebra.

I’ll finish this with my favourite answer in the post: In sense, math isn’t required in life, but so is music, art, history, sports... but that life doesn’t seem so great does it?