I'm not sure whether 'soundex' does the same or not. I usually end up trying so many different variations that I can't remember what half of them were!
I could only find the births of 2 children which you already have, on the British Vital Records ( a CD version of IGI), George born 15th August 1762 and William born 3rd April 1764, both in New Monkland.
I had a we look for an Elizabeth Benny(ie) born around 20 years before the birth of George and the search came up with 4: (1742 +/- 5 years)
Elizabath Bennie, (no date of birth given), christened 15th October 1744
Parents Alexander Bennie and Margret Stewart
Recorded in Cadder, Lanarkshire
Elizabeth Binnie (no date of birth given), christened 22nd April 1744
Parents William Binnie and Agnes Braid
Recorded in Muiravonside, Stirlingshire
Elisabeth Binny (no date of birth given), christened 18th October 1744
Parents William Binny and Margret Wilson
Recorded in Carstairs, Lanarkshire
Elizabeth Binny born 16th October 1744, christened 26th October 1744
Parents William Binny and Marion Wilson
Recorded in Carnwath, Lanarkshire
Of course none of the above could be 'your' Elizabeth.
The one born in Cadder (Bishopbriggs), geographically is closer to Kirkintilloch than the others but that obviously proves nothing as their first two children were born in New Monkland!
Have you got futher information on their children? Who they married, where they went etc? You might have to do some sidways searching!!
Anne