SD1978 "Not when you think it's wrong." So a mum doesn't get to decide if something may be a safeguarding issue?
"You don't need to be involved." Most parents do feel concerned for their kids though.
"Your comment about her being uncomfortable telling him........subtext sounds like you want to start telling her she's uncomfortable doing it. Until or unless she brings it up with you- you don't get to have a say."
This is all completely wrong, IMHO, we do not wait for kids to raise concerns about issues in their lives, we look at situations and see if we think they are safe or appropriate.
There is another room that could be used but it sounds like it is not being used a bedroom for the daughter, e.g. the father has not set the room up with a bed etc. Is that the case OP?
In terms of having a room, thinking of a purely hypothetical child and parent, why would a parent not want a child to have their own room when they visited? Surely the parent would want the child to feel at home.
OP the fact your daughter is so hot on you knocking when you go to her room in her house suggests to me having no privacy at her dad's would be really hard for her.
Hypothetically speaking, to me, it sounds like the parent is either too lazy to bother setting up the room, or doesn't see why a child would need a room in a place they visit weekly or whenever, or the parent is getting emotional support from sharing a bed, or something more sinister.
Sharing a bed as an adult with another adult by consent, whether one is related to them or not, is not a safeguarding issue.
I think for children this could well be a safeguarding issue. It's not a child coming in because of nightmares, or sharing a bed with both parents.