I find it incredibly depressing that the very minute you have a new baby the whole world has an opinion on what you should and shouldn't be doing and doesn't seem afraid to express it.
I think that's even more isolating because it makes people unwilling to ask for help for help when they actually need it.
If you are lucky in the first few weeks you perfect the art of the smile and nod and carry on with your own method of parenting, if you aren't lucky you feel guilty for everything you do and everything you don't do because you are being judged all the time and that can cause huge problems.
Maybe the lady in question has told the op what she wants to hear, as many parents do, I know I've said 'oh I'll try that, thanks' over many different things out of politeness when I have no intention of doing whatever it is.
The fact is that ops MIL is there, actually helping, and is, by the ops own admission pro bf, although maybe not to the same extreme that the op is. The bottles and milk were in the house, I would assume that ops SIL knew that and was happy with it. She is also far more likely to speak to her Mum about how she really feels.
Its very easy to make plans about what you feel you should do when you are pregnant then have a complete turn around when reality kicks in so I would take whatever choices she made during pregnancy with a pinch of salt and take into account the here and now.
I can honestly say in the first few days, or even weeks of being a Mum if I had a text saying 'Oh hi how are you, if you need any bf advice you know I'm here' knowing the sender knew that my baby had a bottle and was very pro bf, I would roll my eyes and think 'fuck off' and I wouldn't go to that person for impartial advice because, in my eyes, they would be incapable of giving it.
Also since the op lives so far away what makes her better placed that the midwife who will be there daily, or the health visitor, or the doctor, or anyone else who can actually see and hear her feelings and problems, if, indeed she has any, to help?