Re: How to avoid spending time with the in-laws
Okay OP; I've read your post and think I kinda get your dilemma.
Lots of people have given you advice on how to avoid the MIL; not sure which you can actually pull off but I'm gona suggest my ways of doing things that may help in the long run.
So basically to avoid offence of any variety you would rather avoid people; I've seen many do this and some have fallen flat on their faces because the in-laws saw it as 'nakre'.
Is a BBCD a British Born Confused Desi?
Do your in-laws like you? Now the reason I ask this is I am aware of DILs that attempt to avoid their in-laws simply because of friction from the dislike and it makes life easier all round if they simply only respond to Salaams? If your in-laws actually like you; I don't think you'll have much to worry about.
Judging simply by the facts you do not work full time, you go the gym and spend time with friends I am assuming that you maybe finding this visit quite restricting. Seriously though, if the only issue you have is the fact you are a BBCD and your in-laws like you then it maybe a case of rather than avoiding the MIL maybe making an effort for the month to spend chunks of time with her that benefit both parties?
Plus on the flip side you haven't said this is their last visit to yours so if you can put some effort in now and get a great reward in the long run (e.g. future visits) you may wish to look at the situation differently.
Trust me when I say I have experience of MILs. My Grandmother is a scary MIL; and now shes old she looks back on her rein as a MIL and wishes she'd done things differently. My own MIL is well erm lets not go there. But what I'm saying is seriously if your MIL likes you it's an easier ride that's all.
Have you spent time with your in-laws in Pakistan? What do they do during the day? Do they have hobbies? Do you have any common ground you can talk about? If your MIL is into sewing and you cannot and wish to learn this could be something you work on together. Same goes for cookery-maybe your husband loves a certain dish his Mother makes? You could learn from the 'pro' whilst you have the chance.
The reason I am suggesting you consider taking a different approach is simply because if your MIL freaks over how you are (e.g. actively avoid her) it won't be pleasant. If you attempt to find common ground and it doesn't work then you've at least tried. Plus no one likes to be under 'pressure' or 'watch' in their own home or have to act a certain way for amount of time.
I don't think it's a good idea to present yourself as a 'bahu' type if that's now what you are and both you and your husband are comfortable with it. My MIL judges all those who wear Western clothing as being sluts. I personally wear Western clothing (if I'm out and about won't make much difference as it's not visable but hey). If my MIL was to visit her son here I wouldn't change my wardrobe for the event as I don't see anything wrong with it. I see my friends about once a month, and take our little girl out twice a week. My schedule is quite predictable and my husband knows this. Rather than you struggling with the idea of having to be the perfect bahu maybe you can 'introduce' the real you little by little?
I don't think this is the best time to get a job; or take up a voluntary post. If you think you may 'offend' your MIL by being the real you have you considered talking to your husband? Sorry if this has already been discussed; but if your husband is fine with the way you are he maybe able to assist you with your dilemma?
How long have you been married OP? Is this the first time you'll be spending time together away from other family?
Also, I don't think OP has an attitude as such; I think it's more of a case of a 'fear' of her real personality being rejected. Many girls go through this. I can remember when I first mentioned to my in-laws in Pakistan that I went for lunch with my friends and I wore Western clothes at home. My MIL looked at me like I was filth. Still does actually. Rejection can often fuel what OP is going through. Of course this is merely my own humble opinion. But only OP knows the real core reason to why she would rather have the minimum of contact.
Good Luck OP; I think you would benefit from having a plan to approach the situ in two ways. The first one of course being the way you want to and the other worth considering like others and I have mentioned is to look at ways of spending time together you both may actually enjoy.