Sound advice from tiny e.a.
What you have to accept, and roll with, is that the words 'wedding' and 'stress' go together like 'love' and 'marriage' - you cannot avoid stress - all you can do is try and minimise it, and enjoy your day.
I now you are looking forward to everything, and you and your mum are naturally sortung everything out - but take a step back and have a look at things.
Your mother-in-law is about to 'loose' her son to another woman. Yes I know it's not as dramatic as that, but believe me, subconciously that is what is going on. What's worse, as she sees it, is that she is providing half the partnership for this wedidng, and being shut out of most of the arrangements, and she is hurt.
Of course you have what you want, and as tiny e.a. says, make her 'feel' involved, and just do what you want - makes life a lot easier.
Th standard 'mother-in-law from hell' is always the groom's, but believe me, sons' mothers can be just as awkward and contrary, so for your fiancee's sake, and your future reltationship, try and get her on side, and just bite your lip if she is a bit awkward, she wil come round.
As for your hen night - let it go, enjoy your friends, and be polite to your 'new guests', but concentrate on you close friends. If the others fee left out, that is not your problem, but don't allow a drink or two to loosen your tongue and ruin your evening!
It wil work out - not stres-free - but you will have a lovely day if you stay calm, stay focused, and relax!
Be very happy!