He needs to pull his weight

Yes you are

at least when I buy legos they will be enjoyed for generations or will appreciate in value if I keep them together and keep the box/instructions.

At the most it's like £40 which really isn't much

it's still useless! The lego set I JUST bought for $120 is already going for $150+ on Ebay. Once it is retired the value is going to shoot up to well over $500! Not that I'd sell it... I might accidentally have a kid someday <_<.

Why do you care so much though?
Her purchase isn't affecting you in anyway. No one is trying to make you buy it

It's not her specifically. It's a mindset. You get 80 million people with the same wasteful mindset and it becomes a problem.

chill