Anandi was no where in the picture till Gehna herself agreed to marry Niranjan
Dadisa Jagya Ganga were the ones who came up with the idea of getting Gehna married and convinced her.
Dadisa just informed Anandi that they convinced Gehna for remarriage after Gehna has agreed to it.
Only after that Anandi spoke to Gehna expressing her happiness and hoped that things will work out well for.
Gehna agreed to marriage because she felt Nandu needed a father figure
Anandi is different from Gehna that way in the sense she thinks her husband will look out for kids and also she is determined to become mother and father to their kids
I think the differences are there in the way they approach their widowhood.
I will not comment on how Gehna fell for Niranjan etc through Gehna they just wanted to show that widow with children can leave her past behind and move on to if she wants to .
I don't think that it is wrong if she moved on in life with another man . Because Gehna did feel that her journey with Basant ended and was prepared to go alone in her onward journey unlike Anandi who feels Shiv is with her and she is not alone even if she can't see him.