My wife has that trouble with EVERY seatbelt. I can sit in the same seat and not have any trouble. The differences is she grabs it and pulls fast and hard which activates the lock.
2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft, HWH Active Air
Charter Good Sam Lifetime Member, FMCA, SKP
RV'ing since 1957, NRA Benefactor Life, towing '14 Jeep JKU Dragon Edition