Elizabeth Cranston McDowell’s father appears to have been Benjamin Allan McDowell.
PRONI have 3 Benjamin McDowell deaths on their wills index. All seem too old to be her father but given the unusual name, they may be related in some way. There’s this for example:
Full Abstract : McDowell Benjamin Nevin of Inniskeen Downview Avenue Belfast company director died 24 December 1937 to The Crescent Nursing Home 7 Upper Crescent Belfast Probate Belfast 30 March to Florence E. McDowell the widow. Effects £5218 19s. 6d.
The will itself should be held in PRONI, in Belfast.
Full Abstract : McDowell Benjamin of 72 Shore Road Belfast retired shipwright died 6 October 1940 Administration Belfast 19 November to Thomas McDowell seaman. Effects £849 13s. 9d.
The above Benjamin evidently died intestate, but his probate file with the admin papers should be held by PRONI. (Not on-line though).