She wants to lead a normal life

She have found out her true life partner in Mahir who loves her so much.

Today she was telling she wants to live with him she expressed she wants to decorate their room paint the wall with her own hands (hope they show it)

Bela has went through from lot of ups and downs and specially dhoka from her closed ones.

She also have right to lead normal life in which she feel happy

Till now as a queen she have fulfilled her responsibility

But being in human world it's quite getting difficult for her as her husband is not aware of her truth.

Mahir is there to fulfil her every wish to make her feel loved which she deserved.

I am very shocked that she wants a normal life. I mean, I did not expect she was so anxious to give up her throne? I am kinda sad about that

Why not pass crown to naagrani maa by assessing juhi suspicious nature

Even I felt sad about that.

It's hard to picture Bela not being a Naagrani. But as is mentioned by @noumi above perhaps she never had love for that power or position. She just wants to lead a normal and happy life with Mahir.

Bela made grave errors in her judgement today. Firstly she didn't see whether Juhi is truly deserving of becoming Naagrani or not. Her childish behaviour should have made Bela rethink on her decision. But maybe she thought that because it's her own sister she is passing on the crown too, she would be much more trustworthy than anybody else (considering that she got betrayal at the hands of two very people she trusted a lot)

She was still going by the image of Juhi she had in mind all her life. Childish, bubbly, stubborn etc but good at heart - That's what Bela thinks of Juhi as. Maybe Juhi was like that. Love for sibling is one thing but what Bela did here is blind nepotism. Other thing that was playing on her mind is to hit all birds with one stone - all her enemies would be in topsy-turvy as power changes hands, she can safely tuck Juhi away in some safe spot (as she mentioned) and help her in ruling. That was rather a naive intention. I mean there are a lot of factors to be considered to pass such responsibility and Bela hardly bat an eyelid at Juhi's bad behaviour... That should be the warning bell for her to see how she would treat her vansh... it's not a domestic behaviour that can be taught or corrected eventually.. She literally pampered her little sister to a favourite toy... I simply can't believe Bela can act so foolish. I'm still not fully convinced...

This Naagin 3 is using a lot of flashback lately. Maybe, they will show that there was more to Bella and Vishaka's conversation in the treasure room where they kept the crown.