Unfortunately in theatre height does seem to matter (speaking as a shortie!). Obviously in real life I am fully capable of being a mother to an 11 year old boy and therefore a mother figure, but in most productions of Oliver the little boys tower over me (I'm 5 foot!). It's a great thing for being able to play young parts for longer but a bit of a bugger when narrow minded perceptions state that a mother has to be considerably taller than a kid, a tall bloke would not date a tiny girl etc. etc.
That said, most of my favourite singers of all time have been tiny - Judy Garland, Idina Menzel, Kristen Chenoweth, Elaine Paige etc. and it hasn't done them any harm. Unfortunately while I think Sarah is very good, I don't think she is in their league.