AIBU for being frustrated with these parents

Keep focus on your child, Op.
She is worried about her friend so make sure your DD stays solidly attending school and keeping up with her commitments and sleep.
Assure her that friend will be checked by the welfare officer if she misses too much school.

My dd had a whole year off once and is now in part time.

She also goes on her phone/gaming sometimes at stupid o'clock in the night when she is up due to her disabilities, it keeps her mind off the pain.

Be annoyed all you like, but you likely only have 10% of the story.

I appreciate you are feeling spectacularly superior here OP and you obviously have issues with this girl and her parents but you know fine well that it is absolutely none of your business. Worry about your own DC and leave this girls parents, who actually know her circumstances, to worry about her. You ‘saying something’ will just lead to you looking like an idiot.

There is also no way the school would have accepted this level of absence without actually having had a number of meetings with the parents and being aware of the underlying real reason.

P6 is peak age for girls to start showing autism symptoms that lead to school avoidance.
Not sleeping at night is also a symptom.

DD’s autistic friend regularly lies to her giving outrageous excuses about why she’s not in school or not attending a social event because she’s covering up her issues amongst her peers. I know this because I happen to be best friends with the girl’s mum.

Parents of autistic kids also often work from home to deal with the constant school absences and appointments.

I wouldn’t judge these parents unless you are so close to the adults you know for a fact what is going on. Sounds to me like you are basing your judgement on what an 11 year old is telling their friends.

I’m not sure what you would gain speaking to the parents. School will pick up from attendance point of view school records are shared as part of transition so would have flagged up previous attendance. My only concern would be my child being messaged to play at unsocial hours but we as a family get around this by turning devices off at bedtime. From experience a few children who’s attendance in primary with big gaps may have got better at start of secondary but then went back into old patterns of anxiety (usually followed by a diagnosis) school refusal numbers are getting higher since covid and you don’t really know the full story.

Beak. Out.

Indeed

That isn’t the answer.

The answer is that she parents her own child and removes her child’s phone at whatever time she has deemed appropriate for her own child.

You don’t get to impose your parenting rules on anyone else’s child unless they’re in your house!

The bar isn't high to be a better parent than someone letting their primary aged child stay up until 2am playing video games on a school night then not bothering to get them into school...

clearly there’s a beef between you and parents if you report to the school the 2am messaging rather than have a civilised conversation to ask for time limits for messaging your daughter

Fortunately the threshold isn't something as lay people we need to be concerned with. All we need to do if we're in any way concerned about a child is to make the report. The authorities then decide at what point a suspicion needs to become THEIR business. No need for the public to go off on a frolic of their own confronting one another, or asking the opinions of other lay people whether a situation they know very little about, involving people they don't know, might be abuse or neglect.

Or just silence your daughters notifications and have phone out of bedroom overnight

You are hearing third hand through your child the reasons why Ella isn't going to school. This does not mean you know exactly what is going on in that household. Ella is either lying to her parents or her friends. Why do you assume you know which one it is? And what's with the 'i think one of the parents is letting her stay home because she wfh'. That sounds like pure speculation on your part.
If he attendance is that low the school will absolutely be dealing with it. Let them figure this out, it's none of your business.

I can practically smell the smoke from the backpedaling

The phone usage, given that is now your concern, is something you speak to her parents about to ask them to impose a deadline to messages in the evening

not the school

You made zero mention of it op

People are offering endless excuses for this family, when it is plain and simple shit parenting to let an 11 be on their phone at 2am on a school night. <Gavel emoji>

This could easily be my child. She is in autistic burn out. Trying to get external agencies involved is exhausting and you knock on doors and get sign posted to a website which has nothing you’re not already trying.

What would you actually plan on doing. Do you suspect shes being abused. If you're going by what your daughter says id keep my mouth shut. Its nothing to do with you.

I'd leave it OP, chances are your DD will make new friends at her new school and the time/friendship spent with Ella will become less as they move on.

Where I would take issue though is with her contacting your own DD at all hours via phone. Either talk to her parents and ask them to tell Ella to stop or, which will probably be the solution, get your DD to leave her phone outside of her room or better still turn it off at night.

Dd had a friend like this. Mum didn’t work so she would always be off school if tired but then she’d be hanging in the park until 10pm with friends the same day. She’d also be Snapchatting to dd at 2am in year 9 and DD’s phone would be lighting up all night (downstairs on the docking station). Her mum once said to me in year 8 “you just can’t stop them messaging and using their phones all night can you?(girly giggle)” and I think my wtf face appeared and we moved the conversation on. Dd will tell me I’m stricter than her (now ex) friend’s mum but it shows I care. After years of friendship dd can see that the friend is being allowed to self destruct her life. She’s unlikely to pass GCSEs. Her mum tells her not to do homework as it’s tiring. They are 14 ffs.

anyway, the result is a fall out between the girls but reality is they’re going in different directions and grew out of each other. Telling a lazy parent to parent better is never going to be successful.

Why didn’t you have your own child’s phone downstairs or in some other way out of their bedroom at 2am.

and if you did, what’s the issue?

The idea of you saying something ?? Are you serious ? Er excuse me I've noticed your child is struggling with her ability to cope with school snd id like to make a completely ill informed and judgemental comment to you about that

The school will be well aware of the child's needs and problems