Hi RJ
Lets do some clinical problem solving here. I am not sure that passive standing is going to do much for her muscle strength and motor control. The question is - are there ways to get her more active so that she develops the strength to pull herself into standing.
You have a child who can sit independently - but is not crawling or pulling up to standing.
How eager is she to move - does she reach out for toys, play with toys? Is she interested in doing things for herself. What motivates her?
Tell us a little more about what she can do in sitting and lying.
What can she do when she is lying on her back?
What does she do when she is lying in prone?
Can she move from lying to sitting?
Does she move around on her bottom in sitting?
Is she bale to pull herself up to standing?
What happens when you support her in standing - does she take weight on her legs?
What can she do with her hands?
Best wishes
Pam