Grace, I am concerned for you - I know this would be hard for any of us, but this is hitting you TOO hard. I think you need to sit down and sort out where your own feelings are in this, and try to not confuse your feelings with THIS situation.
YOU had your baby at 17. YOU stepped up to the plate and raised him. And with hindsight especially, you are glad you did this because of the later fertility problems you had. Now the thought of this pregnancy being terminated terrifies you, because in your mind this could be your only grandchild - you can't separate this girl's situation from your own experience.
This girl is not you. She is not in your situation - she is a different person, with different fertility. Medical science has moved on, whatever caused your later problems may well be easily preventable/manageable now.
Basically, stop projecting.
That said, I do sympathise. I also share your concerns - a 16 week pregnancy (assuming she has the dates right) is no simple thing to terminate - she will have to endure labour. The child will have to be born. All that can be done at 16 weeks, is an early induction. And the dates will need to be confirmed first, in order to make sure the appropriate abortion method is chosen. Plus, she will be counselled.
I do think the initial, "I'll have to have an abortion" reaction is, "I want this to go away without ever having to 'fess up to my parents about it." And yes, there is also a component of, "I couldn't give away this baby."
But this is a knee-jerk reaction, if enough time is taken to just THINK, the decision may change.
But you shouldn't refuse to talk to the girl - you missed a great opportunity to tell HER, "Let your mother know I'm there for her." This is mostly about this girl and your son. While part of this is also about you and the girl's mother too, the parents of this baby and the baby also, are the main issue here. Keep it in perspective. If your feelings continue to rage out of control like this, recognise that this has dug up a lot of rubbing from the past and spread it around in y our head, get to a counsellor and sort it out while it's all fresh and on the surface. If you let that rubbish scatter and bury itself again, you miss a heaven-sent opportunity for your own healing.
And by getting help, you equip yourself to better help this young couple. And if you're there to help them - it could change their decision. You certainly can't change their decision the way you are now.
We've had a couple of pregnancy scares recently. Each time, husband & I had to think, "How would we manage? How will our daughter manage?" with each possible decision.
I was brought up to consider abortion to be wrong. Then I had my own pregnancy scare and had to re-think. When I was pregnant with difficult child 3 my mother told me I should consider a termination - I really wasn't strong enough, she felt. She said she would have used the opportunity if it had been available to her - and I then reminded her that the aborted baby would have been me - did she really mean that?
It's a very emotional topic.
When easy child was a toddler in child care, the director of the centre was a middle-aged lady with no babies of her own, even though she and her husband had tried for years. Then she fell pregnant - there was so much joy! Because she was over 40, she had amniocentesis and found her baby had severe spina bifida. She elected to have a termination at 26 weeks. To go ahead and have the baby, who probably would not survive, would use up most of what little time was left on her biological clock. It was a sad, hard decision and the termination was traumatic. She had to let go of the only pregnancy she had ever had.
She lost the next baby - cervix weakened by the too-advanced termination.
The next pregnancy went to term and she had a beautiful little girl, but the strain of it all was too much for the marriage. Both parents worked as a team to raise their daughter, though.
Her termination was tragic, but it did eventually make her daughter possible.
Termination is a complex, distressing issue and we can't judge other people for having to make such a difficult decision. For the rest of their lives they have to live with the consequences of whatever decision they make. In order to make this decision wisely, and independently - they need you in one piece, holding yourself together and supporting them. So get yourself together - after all this time you ow it to yourself. These kids have given you this chance.
Marg