Just to clarify- this is not a MIL bashing thread. We get on really well and she is a lovely kind woman. But....
She has form for copying me which doesn’t generally bother me but this time I’m really pissed off.
We have a family wedding coming up next month. DP needed a new suit so he went out and got himself one. 2 weeks later MIL and FIL also go and get a new suit. As she’s showing me I notice it’s exactly the same suit that DP got. She laughs and says ‘Yes but FIL’s suit is slim fit not skinny fit like the one xxxx got.’ Still it’s the same colour, brand and style so is the same suit in my opinion. He’s also got the same style shoes to go with it and the same colour shirt to wear with it. DP was a bit annoyed as they will be dressed pretty much the same.
Fast forward a few weeks and MIL asked me what I’m planning on wearing to the wedding. I show her the dress that I’ve got (navy lace) and the nude shoes and bag to wear with it. She said ‘that’s nice’ and not much else. A couple of days later she said ‘I think I’m going to look for a navy lace dress to wear to the wedding’. I was a bit 
but thought no more if it.
Today she’s sent me a picture of the dress, shoes and bag that she’s got and it is pretty much identical to mine. The whole bloody lot of it!
Why? Why? Why? Does she not realise we are going to look like a load of twats all wearing the same thing? I mentioned it to DP but he became quite defensive saying if it bothers me that much I should change my dress. AIBU to be so pissed off about it or should I just take it as a complement?
Also I’m now debating changing my dress and not ever telling her anything again but I absolutely love it and will struggle to find anything else I like quite as much.