It's okay to have daughter in her 30s and still single. Maybe she wants to save money to buy house for herself and fur babies. Maybe she's busy with her career and doesn't have time for relationship. Maybe she's skeptical about marriage or simply hasn't met someone she wants to marry. Maybe she's been through tough times and needs a break to heal her soul.
Whatever the reason, you don't have any right to judge. And never even think it's your fault. You might give a birth to her, but you're not responsible for her own choice. You've done your part. You feed her well, teach her well, and raise her well. It's more than enough to expect from parents.
Stop pressuring your son and daughter to push their daughter to get married soon. That chain of endless pressure is so burdensome. Why can't you let your grandchild be at peace with her singleship status? She's totally chill until you ruin it with your annoying 'when'.
Dear everyone saying bullshit like "I just want to see her happy",
You know what? If you really want to see her happy then just leave her alone. Thank you and fuck society. She ain't live up to your expectation. Nor should you.