Congratulations on your soon to be wedding.
I don't recommend a 9 day liquid diet, at any time, but particularly, when you're trying to get ready for your wedding, as it can have some pretty adverse/unwanted effects.
Seems that the best thing to do is explain to your mom that you really appreciate the wonderful meals, but that you're gaining some unwanted weight, so you need to cut back a bit. Ask if she can slim down some of those favorites a bit. The alternative is to simply load up on the veggies and salads and eat smaller portions of the higher calorie foods she's providing and/or get in more exercise every day to work it off.
Here's mytwo cents~ Try to control your calorie intake.
I did a liquid-diet for 9 days then really watched how much I ate … lost about 5kgs in 3 weeks … those 9 days were a pain as my bf eats all the time … so it really depends on how much you want/need to do it. I think with 6 weeks, you can just adjust the amount you're eating and it'll be possible. Good luck!