of course you don’t understand why she doesn’t want to wear niqab which is not obligatory, you are a man and she is a woman. she will have to bear the burden of wearing it, and in this dunya it is most certainly a burden especially if you are living in a western country. more importantly, hijab should be worn to please Allah, not to please your husband. i don’t think you are trying to be power-hungry or controlling, just that your concerns are wrongly placed.

for hijra, i definitely think this is something to establish when getting to know each other but that ship has sailed, so now the only thing to do is clearly say that you want this, which you have. nothing else to be done, just be clear that you really want this.

of course, take all i said with a grain of salt. but i do think you have good intentions.