If there is nobody at home during the working week, what then for a puppy/adult? Listen to mum - she's right. Now is not the time to have a dog. Right now you may feel you have the time to deal with a dog, forget about a puppy because they MUST have somebody there pretty much all the time, but in another year, next week even, something else will enter your life and you'll have another dog that has to be found a new home.
Perhaps, once you are through your schooling, and out living on your own, you might be able to have a dog - depending on your accommodation, finances and most importantly, time available. Having a dog is a full-time commitment, as you should have already realised if you did have a dog before and it didn't work out.