I’m pretty sure they don’t refund anything, they’ll give you that 300 towards the new lease / purchase, but if you are just turning the car in you’ll get bubkis.
Is your aunt not taking another car at all? You can ground your lease at alternate brand dealership as well if you are taking another lease and that dealer can return the car to the BMW dealer they work with.
In most cases the local BMW dealer should take the car and only at the height of panic during initial lockdown did I hear that they were full and were not accepting the cars sold by other dealers.
You can call few BMW dealers around and let them know that the car is way under mileage and in perfect condition (if it is) for them to think about adding it in their certified inventory and that might open an option for you in your area.
I just turned in my BMW yesterday with 3 months remaining on the lease and only 10k miles on it. I still have my $300 from my prior lease. Since I switched to Audi, I will be interested if I get another $300 for the unused miles or if just the original $300 credit was on there. Will let you know when I get my final statement.
So much negative equity in BMW Leases - dealer wanted no part of it (even with 10k miles on a 2018).