Green’s Dictionary of Slang

1. a good-looking woman [SE bloom].

1861		Bell’s Life in Sydney 2 Mar. 3/3: Another bloomer known as Lizzy Burns swore that she saw the prisoner take the watch .
1887		‘’Arry on Angling’ in Punch 30 July 45/1: Bell’s a bloomer.
1895		Coburg Leader (Vic.) 13 July 1/6: Who were the two bloomers on the tandem bike that came to grief [...] on Saturday last?

2. (Aus./Can.) a newly arrived immigrant [they bloom in their new environment].

1900

Boy’s Own Paper 17 Nov. 111: A ‘new chum’ or ‘bloomer’ who settles in Canada or Australia.