i think my download speed should be better ??

Let me guess because that is about all anyone can do at this point. 1. Your machine has an older ethernet card than her machine. 2. Your machine needs a driver update for the network card. 3. You have a bad cable connecting to the router. 4. You have system updates that have messed with your network settings. 5. You tried to "modifiy" the default settings of your network card and you should have left them alone. 6. You need to check the priority settings of the router itself. (Some have that feature.) 7.Your ethernet line runs across some AC lines on its way to the router. There are other possible issues. A good network service tech may be in order. The first check I would do is see what speed you get if you connect to the line running to the other computer!

PS - your "general rule" is only correct for SOME internet lines not all, however if your other machine is seeing a much higher download the rule may be "in the ball park" for your provider. The speed you get is generally the speed you pay your provider to obtain!