My little cousin asked for an Amazon Echo believing that she could ask it to play any song, she was disappointed in finding out she needs a subscription for that.

I’m considering to teach her how to maintain a digital music library on her phone she could then play on Echo trough Bluetooth but in the last years I had little experience with Android. I need recommendations on a good and ad-free music player app with easy library management and maybe a great looking UI too. Free and paid options are both good but subscriptions are a deal breaker.