How do you interpret this message?

[BillLius]

Someone in the household received a box of flowers with this message attached.

Who sent the flowers or who received them?

Happy birthday, Darling

Mum
xxxxx

Happy birthday, Darling Mum

xxxxx

Happy birthday

Darling Mum
xxxxx

I thought the giveaway was the capitalisation of Darling, in place of a name, and Mum indicated the recipient was Darling and the sender Mum. I agree with you that the grammar was important and whatever spacing was used when the order was placed has been lost.