Not sure where the OP has gone, but I tried a plant based diet (I didn't change anything non-food) for Lent and while it was interesting and tasty and a good challenge, it meant I was doing pretty much all the cooking and pretty much all of it was from scratch, and it was more expensive than non-vegan because of the things that my family will eat.
So while I'd do that for me, for a short time, I'm not doing it long term!
I would tell her she can have an allowance for HER toiletries and the rest of you will carry on as you are, nothing else in the house will change, and she can start off by planning and cooking one meal a week as vegan.
If she eats a variety of vegetables and pulses and you are satisfied she eats a balanced diet, you might consider increasing that, but if she's also a fussy eater then no.
If its pizza treat on saturday night a vegan version can be bought from supermarkets.
I found it impossible to get this kind of thing in a vegan version. The only real ready meal options were a few stir fry dishes, a very few Indian meals, and burgers/sausages. Maybe you shop at different supermarkets (we are in the Waitrose-free North).