Dictating what happens at our home ref bedrooms

[Spanglyprincess1]

So current two youngest Dsc share 8 (dsd) and 9 (Dss). And eldest Dsc (12 dss) is on a daybed in the dinning room. All is fine. Plans are when youngest dss goes to high school to swap rooms so two dss are upstairs and dsd is on daybed. Logic is she's too young now (has medical conditions) plus is staggeringly irresponsible. We have them overnight 1 day in week, eow and half school hols.
Other option was to have three is largest room and split with a room divider but dp didn't want that.
Last night their mom called dp n said she's not happy as middle one dss is sexualised now and wants two boys upstairs or is stopping contact.
This isn't okay for dsd at all for medical etc reasons and we don't wnat to do that. The room arrangements and changes when at high school were all agreed at mediation last year. The children are happy and we have had no behaviour issues (their mother has at her home but we haven't).
Surely she can't dictate contact like this?

Seems to me that this isn’t really about bedrooms.
We are having issues with DSDs mum just now. She has made plans for DSD on DHs weekend which throw our Christmas plans out the window (DSD is not allowed EVER to see her dad on her birthday or Christmas) and is expecting us (by that she means me) do drop everything and do all the running about to facilitate her. And is now crying that she has childcare problems because I am point blaming refusing to do it.
She doesn’t seem to appreciate that I have exactly zero obligations to her or DSD so when she dictates from on high I come over all uppity and refuse to pander to her. I have my own child to prioritise.
However, if she approached things with humility and manners and actually engaged in a conversation rather than acting unilaterally, she would find that there’s not much I wouldn’t do to help her and DSD because I do actually care very much about DSD, I just don’t want to sacrifice my own sanity.
So OP, I can completely understand how you are feeling about this, although I don’t have anything to add to what PPs have said about the bedrooms.