I lost my jack during an upgrade last year, but I also got free buds with the phone. I thought I would hate them, but I actually listen to more music now than I ever did before because it's so convenient not to be wired to the phone.
We also have a couple of good over-ear wired headphones in our house, so I bought an adapter to be able to use them. I bought a no brand one for a few pounds off Amazon (just to try it out at first, really), so probably the DAC inside is not doing them justice, but they still sound great, much better than the buds. It still works fine now, so until it breaks, I'm pretty happy with it. If it breaks, I won't be happy with it, but then I'll probably get a better one.
For your sister, maybe try a different adapter if the connection's bad, assuming it's not filled with lint or something. Google assistant has only ever gotten in the way of everything for me, so don't enable it - not sure what to do about that.