i think if you approach her on this its going to end up being a big argument, lots of hurt feelings, and plenty of gossip about
the pair of you.
you don't want your wedding to be remembered as a big battle of the brides!
those who know and care about you will know what she has done, and in truth she may not even realize she is borrowing your plans. as for your being in charge of her wedding, you either just tell her no! that you don't feel you could give her the full attention she deserves as your own wedding is taking up so much of her time.
or you say yes i'd love to help you, and then help her come up with some unique and beautiful ideas for her wedding day thus leaving yours intact!
as excited as you are about your plans i hope you have learned a valuable lesson, don't brag about your wedding! and i'm sure you weren't 'bragging' but you know what i mean, you never, ever divulge specific details. you answer everyone's questions in generalities.
thats not going to help you now and about all i can say is this, you are obviously a 'crafty' type girl, someone with lots of great ideas, so tweak your plans just a bit to make them uniquely yours - again!
meanwhile you aren't the first bride, nor the last, that will think gosh i'm going to have an evening candlelight wedding at this venue! in other words you don't own the right to that style wedding, that time of day or the venue - so now you have to rethink, revamp your wedding plans.
for example you were going to have a candlelight wedding - i don't know what you were going to do but if you hadn't thought of it then why not go all out and have huge candelabras, sitting on glass mirrors. if that was what you had in mind then change it over to hurricane lamps and votive lamps with silver sparklies scattered all over the tables. or don't have candles now! use fairy lights, rope lighting, chandeliers! there are lots of ways you can change it out, and you still have lots of time to deal with this kind of detail!
see what i mean? but whatever you do, keep it to yourself!
i'm surprised any venue still allows candlelight! pretty much everywhere in our little corner of the world has banned candles/flames of any kind.
whatever you do, however you change your plans, keep it to yourself and have a very happy wedding!