Wedding/dealing with mother

I'm putting this here instead of the wedding board as it's more a "mum" problem than a wedding problem.

I got engaged 17 months ago and we are getting married in a couple of weeks. Invitations went out in January and we sent save the dates out December 2015 when we booked the venue.

We are on a budget, while all of my sisters had £20K + their dress handed to them I've had £5K handed over and that includes the price of my dress (more about that later). Our wedding budget is £15K and it's been spent, we've only just afforded it without getting into debt and we've spent £14,890. There's not much left and that's fine, our numbers have been confirmed with the venue and the bill has been made up and will be paid this week.

Now I told OH I didn't want to involve my mum, just collect the RSVP cards and I'll construct a table plan, I know most of the in fighting and family politics and I'm capable of sorting it out. We made a table plan, tweaked it and OH INSISTED that I run it by mum.

We arranged to visit home last night to show mum the table plan, she went out so I texted her and asked when she'd be home and the answer was basically I'm out with my friends just leave it and I'll do it. We are so close to the wedding that isn't a possibility so I told her no, she looks at it tonight, she visits us on Thursday to do it or she's not involved at all.

So she starts asking where I've sat people and who I've put where and complained that I've put uncle X (not my biological uncle and not actually invited by me, that's a story in itself). I told her "oh with my favourite uncle, your best friends, his son and one of my nieces who his son gets on with" and she complained "you've sat him with boring c*nts". Well mum it's only for a meal.

So then she starts listing who she wants where and I'm trying to explain that tables are only so big and she wanted them mixed so it's 2 couples from our side per table, she doesn't like that. So she asked about her cousins from one side of the family and I said none of them RSVP'd. She said they have a habit of not RSVPing and then turning up so I said "well they won't get fed". I explained numbers are finalised, tables are full and to add them on would cost £80 a head for the meals alone, they'll need a table, chairs, linen, a centrepiece and stationery and I'm not willing to add them at this stage, she literally ignored me and kept talking.

So she got in touch with the cousins (we only have one address for all 4 and partners but I send 4 day invites, 3 evening invites for their kids and partners, 4 save the dates and they have me on Facebook). They said they had no idea I was getting married and not one scrap of wedding stationery made it to them - colour me sceptical. Anyway mum has invited them to the full wedding, she texted me to tell me at quarter past 11 last night!

In the car on the way home from mums last night my fianc! was all mouth "oh if she tries to add people on I'll tell her no and I'll tell her it's evening only blah blah blah", at 11:15 he was suspiciously quiet and this morning he just asked what I texted back (mum the numbers have been finalised and the tables are full - she hasn't read it).

And now for the back story, I'm the middle child born during a very messy divorce and mum has no interest in me, never really has. I had a heart transplant and she was interested then but only because of the attention it got her. She has a weird relationship with all of us girls (the boy doesn't talk to her at all). Every time my wedding comes up she talks about my sisters wedding, even showing off photos of my sister in her dress at my dress fitting last week.

I've always been the burden child, mysterious illness growing up and the transplant (she loved that). She looked after me a lot and claimed carers allowance up until last year but got bored so now I pay more for private care. My (step) dad thinks she still looks after me during the week and lets her off with paying almost nothing into the house (they're both self employed). It's recently emerged that mum is probably having an affair with the uncle im not related to that's sitting with the boring c*nts. My dad is basically putting on a facade until the wedding is over.

I genuinely think she has mental health issues or some sort of bonding issue with me. She's never really been "mum" like to me like she was with my sisters (not my brother, he was ignored then sent to live with our grand parents). Even when she was caring it felt more like a nurse-patient relationship. I don't hate her or anything I just hate what she's doing to my wedding. She's literally not spoken to dad for a month, has decided that she's divorcing dad but he's to stay at home and pay the bills because she's not selling the house and wouldn't be able to afford to buy him out, she hasn't told dad this yet and doesn't know he wants to divorce her and knows about the affair.

So what do I do? She's went ahead and invited these cousins, I have no space for them now and no money to pay to feed them. She might offer to pay but she's fly with money and I will probably never see it (she owes me £500 for something I paid for her 2 years ago, she asked me to buy it on my bank card as she doesn't use her cards online). I don't want to get into debt :money: I'm happy for the cousins to come at night but I'm not willing to add a table in at this stage and don't think my linens guy will be too happy with having already been paid in full adding on extra places.

Despite OH mouthing off he probably won't say anything and he is a bit of a push over.