Welcome to HealthcareMagic forum.
Please do not worry.
Many of the normal infants can have delayed standing and walking milestones achieved only after 1 yr of age.
As of now first and foremost you should get your child assessed by a pediatrician
to rule out any neurological or muscle weakness
( since there is a history of spina bifida
However if she is sitting and crawling I do think that most likely there is no disability
and just a physiological delay .
In case there is any weakness , physiotherapy
can improve her limb strength and achieve her milestones.
Please do get her evaluated to be on the safer side .
Wishing her good health.