rider weight for full sus?

I've a friend who wants a lightweight xc, trail bike as they find it hard to muscle their existin bike around due to their size. Basically about 5.10 but only 8.5 stone. Is it worth getting a short travel xc full susser like an anthem 2 or will they not be heavy enough to get the use from the rear suspension? At the minute they're lookin at carbon scott scales etc.
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Carbon 456
456 lefty
Pompino
White Inbred
If you look at Specialized range (Safire, Myca) for female bikes (build is often tall and low weight) they have the same shocks and folks as the male bikes. You could look at some other makes and probably find the same thing.
http://www.pinkbike.com/photo/1844919/