Church singing puts some people off,because the melody line is often scored for sopranos or trebles. In a church choir, lower voices can take the harmony parts, but the poor congregation get lumbered with a line that for many voices is not in the comfortable range. Dropping a whole octave will usually be too low and you'll end up growling.

There isn't really an answer to this for your friend, other than to realise it's not her fault that some hymns are pitched too high. Yes of course, there are exercises and techniques that will help her extend her range, but she shouldn't let church hymns make her feel inadequate.