Is this bonkers SIL behaviour or am I overthinking it?

Indulging rudeness, paranoia, or unreasonable behaviour is not the "correct" way to deal with anxiety.

Perfect way to deal with it.

A firm no from me.

I mean it could go the other way & feed into it?

Perhaps worth seeing exactly what she wants but I think I'd be asking her to show/explain how she wants things doing.

This made me laugh to be honest because I remember doing similar. It’s first baby anxiety and yea it’s way OTT. I remember people thought I didn’t trust them, but I barely trusted myself. It passes, but on this occasion If it eases her worries then try not to take it personally, I’m sure it’s not a reflection on you.

I can understand and if it soothes her worries I don't know why you wouldn't just help her out, it'll only take 10 minutes.

Some people, even those who've had children are utterly crap at changing nappies though. I've seen women lifting babies bums up with their ankles, wiping back to front on girls, leaving very obvious poo smears on bums.

Also some people bottle prop or think the best way to give one is to force the baby to chug super fast flat on their backs. She might be pace feeding?

First of all, read her post properly, the “toddler” is an 8 month old baby.
Secondly, stay well away from anyone who struggles with anxiety because you really haven’t got a clue how to handle it correctly.
Attitudes like yours literally increase someone’s anxiety, the only person who can lessen it is themselves. You can’t bully it away 🙄

It's weird but I don't see the harm in easing someones anxiety.

The feeding I get as my 7.5 month old is a nightmare with bottles but we can get her settled with milk a particular way so I do show folk that. Not to insinuate they can’t do it, more for their sanity with the wee headstrong bugger 😂

the nappy bit though, that’s bat shit!

It's not about your competence at all, it's about her anxiety and the fact that she's done it all without help so far.

I thought she had a DH?

Please do not do this. Do not enable this level of anxiety. She needs to realise she's gone too far, the child is a toddler and you are a mother! Did she 'audition' your brother for the role of father?!

I really wanted some time away from my baby but couldn’t bear anyone else looking after her “just in case”. Think of it as giving her the gift of peace of mind, soothing her fear. It’s easy to forget some of the anxiety that comes with your first born child (I had PND which made it worse).

It's weird. It sounds like SIL has some weird ideas - maybe that an 8 month old will be totally upset if she isn't changed or fed exactly the same, or that having it done differently will hurt her. I think though going along with it is the right decision, because SIL feeling more confident in leaving baby will be good.

I’d be slightly concerned about her TBH. That sounds well outside the normal anxiety about leaving your baby. I’d go along with it but hope you’ll be laughing about it together when she has more children and her PFB is eating dirt with one hand and sherbet with the other.

I would rescind the babysitting offer.

@BirthdayRainbow Yep I'll make sure she's aware of how I do things as I know it will be difficult for baby to adapt straight away! Thanks for the heads up

It's harmless enough and if it makes her feel ok about leaving the baby then just go along with it .
To be fair one of my children's grandparents changed a nappy - it was the first and last time after I discovered she did it up so tight it left deep red marks in the babies skin and was the reason why he spent hours screaming !
She is probably way over thinking it all but best to put her mind at rest

I wouldn't agree to it as it will feed her anxiety and controlling behaviour. She is very welcome to leave you instructions but beyond that she either trusts you or she doesn't - her call. If it was a new born, maybe, but not at 8 months old.

She's not being bonkers - this is very common in first time mums who haven't put their baby in nursery or with a childminder regularly, and sounds like she has been looking after the baby all the time. It's due to anxiety, and due to having been with the baby full time since she was born, and it's also a first step for her to learn how to let go.

It's definitely not personal and I think she would have asked it of any family member babysitting. It's almost not so much "testing" you but somehow psychologically feeling that she's taken care of the aspects that she feels connect her to her daughter. (I think you can feel insulted if she asks to observe you after her baby has been to nursery and has had 3 babysitters before you.)

You don't have to agree, of course- you could withdraw your offer. However if you agree you would be helping her and your brother - to help her let go a little - if you agree to do it and to babysit of course. Also, she might pick up some tips from watching you as you have three kids.

this is beyond batshit

It’s not a criticism of you - it’s just normal “crazy” from a mother with her firstborn…. You’re doing a lovely thing anyway, I assume because you want to help her, so let it go :)

Dear SIL, I have 3 kids, your PFB will be perfectly safe with me, you don't need to test me!

Wow that is terrifying! He must have been boiling and I can't understand how everyone else thought it was ok!

Anxiety is not an excuse to act however you want with everybody else's indulgence. I would not be entertaining this rudeness.

In fairness it's the OPs thread so the support given is directed to her interests not those of the other woman. I don't think its in the OPs interests to look after the baby at this time. Too much risk of her doing something wrong in SiLs eyes which could lead to long term damage to their relationship. OP has offered herself as a babysitter not an emotional support to help her SiL over this level of anxiety. It doesn't seem in anyone's interests to go ahead with this.