My view is a bit different from the rest and probably not popular, but its my view.
I wouldn't want my daughter to be in your position because I think it's really hard being a single parent.
Your mum has probably seen you struggle bringing up your son on your own and naturally wanted better for you. For your child to be raised by two parents in a stable family unit.
It's a tough job being a mum and I imagine even harder as a single mum from what I've seen.
You were young when you had your first child and maybe your mum thought you'd have learnt from that. So I can see how she feels disappointed. The fact that your mum said she feels ashamed shows that she expected better of you and had higher hopes, because if she didn't love you, she wouldn't be bothered.
Look at it this way ... you're bringing a new life into the world and you've only known the father for a couple of months.
You really don't know him at all and this is how women get forever linked with undesirable men, because they have a child together and have to maintain contact.
I personally think choosing the man who will be the father of my child is a very important decision.
People will say it's 2016 and indeed it is, but that doesn't mean individuals must change their own personal values and beliefs.
I'm sure she'll come round in time and accept her new grandchild.