Worried about my sister's pregnancy

My sister is 40 and wanted 1 more baby. She had a miscarriage and a D&C and got pregnant 3 weeks after that. She just had her 1st ultrasound at 6 weeks and she is pregnant with identical twins. The miscarriage almost destroyed her and now at her age with the quick pregnancy turn around I am worried something is gonna go wrong and it will be worse this time. I've had 2 miscarriages and my OB stressed waiting a full month minimum but preferably 2 or 3 to try to get pregnant again since there can be more complications getting pregnant too soo after a miscarriage...especially after a D&C which I had 1 also. Identical twins already are riskier then adding her age and how fast she got pregnant I am scared. I am supporting her and keeping my my fears to myself but shes my best friend and her kids are like my own and the miscarriage broke her kids hearts and near broke her. I'm hoping the best but have a gut feeling something is off and I hope I'm wrong. Edit: her D&C was 4/4 snd they have her conception date at 4/22. When I had my D&C they wanted me to wait min of 6 weeks to try again because it increases the miscarriage chance if the lining doesn't have time to fully heal and rebuild. Thats my worry is it is so close between procedure and conception.