I thought the most likely John Loosley on the census was the one b 1812 in Princes Risborough and was married to Mary Lane (at least, that was her maiden surname from the GRO indexes of their children's birth registrations.) One of their children was named Jesse Loosley (b and d in 1846), which made me think it is extremely likely this John was Sophia's brother. John Loosley had a brother living with him in 1841 and 1851 - William aged 35 in 1851 (so 1815/16) who was unmarried.
Annoyingly I can't see a marriage for John and Mary (she was 31 in 1851, so likely married after 1837. First child seems to be Oliver John b 1840 d 1841). I suppose it will turn out they married in the first half of 1837!
I had hoped the record would tell us John's (and hopefully therefore Sophia's father's name.