Aibu? SD unnecessarily attending school

[ToddlersConspireAgainstUs]

Long story short, DH is not a key worker and is pretty much off work (teaching assistant, works from home but there's not much to do ifyswim), SD's mum is a key worker, as is her DH. Neither houses are showing symptoms so there's no need for isolation, but here were following strict social distancing, no going out unless for essentials and no seeing family. As far as I know, other than work, it's pretty much the same situation... so all should be well?
Not exactly, SDs mum wants to send her to school as obviously she needs child care when she's at work (SD is primary aged) despite our household all being at home 24/7 now. They have shared care and everything is pretty amicable, SD is just stopping longer at each house to minimise the need to moving too often between homes.
I can't help but feel SD shouldn't be going to school and potentially putting both families at risk (Not to mention pressure on school to provide staff for a child who doesn't need to be there) when one parent is perfectly able to have her but her mum feels differently. AIBU to put my foot down and demand this stops? Non of us fit into any at risk categories but I do have a young DD and clearly non of us want to be ill if can be helped. I'm trying to be rational about the whole situation as it is and I don't want to create a fuss where there is no need for one, some impartial opinions maybe ?

Your DP could ask and have an adult discussion about it - demands usually get peoples backs up.

There has been a discussion, SDs mum is adamant she doesn't have child care, SD must go to school or she can't work. That's clearly not the case when her dad is at home all day now. DH doesn't really want to cause conflict over 'nothing', but I don't think is nothing and as the adult conversation over this hasn't worked it is something he should be making demands about.

However, I just wanted some other opinions on whether I'm being reasonable or not as she's obviously not my daughter and usually I don't expect to be party to decisions made about her, but I think this decision effects everyone

I think that you are right that she not be attending school. However, it is your DH that needs to sort this out with the mum. You cannot really demand that anything changes, but you can have a serious conversation with DH about it and make your feelings clear to him so that he can speak to ex.

It sounds like he is in denial or does not fully understand the severity of the situation if he thinks this is a fuss about nothing.

Maybe between them they can cover most shift, so it would only be occasional.

Are you suggesting she only comes to you when she needs childcare, so transporting her back and forth, or her staying with you for an undetermined time?

How far away do you live? If the suggestion is to stay with your for 2 weeks when she only needs childcare for two afternoons, I can understand she feels that she can go to the school for these shifts.

The current arrangement that's been made to avoid moving between houses too much is SD spends a week at each house, as opposed to half a week at each. Her mum was happy with this. It's since transpired that she needs to send SD to school for 4 days a week. The days SD would have to go to school fall on the days SD would ordinarily be with her mum, and whilst she is happy with the week each arrangement she won't just swap contact days with DH so she just had SD on the days she's not working as then she says she would miss out on 'Her' time with SD. I understand her not wanting to miss out on time but at the same time I feel these arnt ordinary circumstances and it's unfair to put other people at risk it. She's not normally unreasonable about things but I don't think this is helped by her reading too many 5g conspiracies so not fully taking it seriously as a virus , DH mother has COPD as well having previously had chemo so is very high risk so we're taking it pretty serious

I don't think you are being unreasonable and I don't think it is wrong of you to expect a say either, these are not normal times when it is "none of your business" what their arrangement is, the risk attached affects all of you. You could try reassuring her that you won't be asking for maintenance if you end up having her more, but it is the sensible thing to do.