My daughter’s best friend was absent from school today, and she had a really hard time. She said she was “nervous” to ask anyone else to play with her.

Any advice to help her make friends? Or feel more comfortable asking other kids to play with her/join in when they are playing? It broke my heart to see her so sad. Perhaps a book recommendation?

For reference, she is 4 and has always been quite shy/slow to warm up to people.