don<t make a big deal out of it.
let mil pick something she likes, make her happy. its her sons mehndi. ur her bahu.
let her hsow the world that you are so caring and obedient, that you wore what she wanted.
it is too ealry in your relationship to start crossing paths with your mil. also do not tell your husband aobut his either. they will rmeember these things.
who cares if one day you owre somthing she liked insteade of what you liked. you still have 2 other days. look at the big picture,m what is important. that you are getting marreid. that his family is accepting you and giving you their son. think how lucky you are. think happy thoughts.
i don<t think she<ll pick something that makes you look bad on purpose, she will want to make her bahu look gorgeous. she has some armaan too. don<t diagree with her, there are lots of of those that will come up. do what she wants, she will start to love you even more.
She shouldn't have to show the world how 'obedient' she is, when will we stop this bizarre obsession with 'what will people think?' There should be give and take on both sides, not DIL just blindly having to put up with situations she isn't happy with.
They are lucky getting a new DIL as well. I take ur point about not making a big deal about everything but really if she is the one wearing it if she doesn't like it she shouldn't have to.