Ok I already know I am being unreasonable, it's DPs sister, but I reeeeeeally don't want to go!
I don't like weddings anyway, but I'm especially dreading this one. His sister is just awful, acts like a spoilt princess at the best of times but is now the bridezilla from hell!
If we visit his parents and she is there, we can't mention buying our house or she gets cross that we aren't focused on her wedding, and yesterday when his mum started asking me about any ideas we've had for our wedding, she gave me the most awful look and loudly announced that there would only be her wedding this year so her mum should be focusing on that, not another one that isn't booked yet! I didn't want to tall about our bloody wedding, getting married is something me and DP will do but I am really not arsed about wedding planning and it will be very, very low key, so I resent being looked at as some awful thunder-stealer! Herr attitude whenever the conversation is about anything other than her wedding is just truly grim.
On top of this, I hate the way I look and we are buying a new house as we speak, so money is tight so I'm stressing about my outfit and what I'm going to wear. She said that she expects her guests to wear designer outfits as anything cheaper would ruin her day and the photographs 
I have already managed to get out of the 3, yes 3, hen parties, but my DP really wants me to go with him to the wedding and take the children so I don't feel like I can say no.
Although she had never been directly hostile to me, I get the distinct impression that she really doesn't like me, probably as we are so different, and I feel as though I won't measure up on the day,and she'll mock me for my outfit etc.
Would it be unreasonable of me to contract food poisoning so I can't go?! only half joking