The garden is a popular place, which offers people the chance to sit and reflect while visiting or staying in the hospital.
"We know how special the garden is and everything we raise from this goes straight towards keeping the garden looking wonderful. People trust that the money given goes to the garden."
She was saddened by the event, as it was a special time of year for those who had lost loved ones.
"We usually get 1700 doves on the tree and expected to reach that this year. It is a very special occasion and we bless all of the doves at the hospital remembrance service."
Reverend Walker had now got a new donation box, which would be harder for people to walk away with.
"It is a bigger box, which you can't just take the lid off and walk away with the money inside."
She said this had happened in previous years but not to this extent.
"We have had a wee bit taken but not this amount so quickly. The tree only went up on Saturday."
She hopes the money will be returned to the hospital as it is a special time of year for those who are remembering loved ones.