 Donna is shocked when her estranged father Derek ( Clarke Peters ) is admitted to the hospital and diagnosed with cancer . He dies soon thereafter , and when dealing with his effects , Donna learns that he unknowingly fathered another daughter . Though her half @-@ sister is recently deceased , Donna meets her half @-@ niece Mia ( Jada Wallace @-@ Mitchell ) , who is being raised by her grandmother , Patti ( Barbara Drennan ) . Within weeks , Patti also dies , and Donna decides to adopt Mia . She and her friend Maria ( Phoebe Thomas ) compete for a ward sister position on the general surgery ward . Although Maria is the successful applicant , she realises that Donna needs the job in order to support Mia , and withdraws her candidacy so Donna is appointed sister . Donna falls in love with agency nurse Kieran Callaghan ( Barry Sloane ) , and is devastated when he is called to serve in Afghanistan with the Territorial Army ( TA ) . Kieran asks her to marry him , but Donna refuses , terminating their relationship with the intention of giving Mia stability . When Kieran is injured by an improvised explosive device ( IED ) , Donna reconsiders , supporting him through the amputation of his leg . Upon learning that he will be transferred to a rehabilitation unit in Liverpool , Donna resigns in order to move there with him . 
