GTT question for my sister?

[Lisa]

My sister is currently 35 weeks pregnant with her first baby.
She has not had a GTT done.
Is it normal for her to have not had it done? I had it with all of my children (apart from Noah) and it was around the 28 week mark from memory.
So... is it normal for it to not be requested for some women? Should she enquire about having it done now or would it make no difference this far in?