What a hard position for you to be in. Hugs and congratulations on your pg.

Firstly, as the others have said, your sister is dealing with a very deep, very painful grief. A grief so intense that she is not physically able to connect with you or your pg, because you have the one thing she would give anything to have, and that cuts her like a knife inside. I dont think it is wrong or unfair that she resents you at this time because at the moment she can only see the fact that you are pg and she is not, when she should be. But one day perhaps she may regret the way she is treating you now.

Of course it isnt fair that your pg is being ignored when it shouldnt be. I would be devastated too, and I guess there is no win-win here. However your mum should be doing more to celebrate your pg, because this new baby deserves it. You should not feel bad in any way that you conceived this baby when you did. You have a right to live the life you want, and you did consider her feelings by asking your mum to tell your sister.