Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.

 

Praying istikharah is recommended. As a result of your istikharah is that your mother disagrees and discourage you to do this step. It is a sign that resignation in this case is not good.

 

Praying istikharah is done in situations where there is no indication in the Shari`ah to show that such a matter is prohibited or obligatory.

 

In case it is prohibited, avoidance is compulsory and no istikharah is needed. In case it is obligatory, you have to do it without praying istikharah.

 

Almighty Allah knows best.