I know of a child that was around a year old using a helmet. I don't remember much about the encounter but I know he was older than my child at the time who was 10months and when he had it on, I asked about it. He was older than a year. I think you should pursue it even if it may not do much now. Try not to be hard on yourself, you went with the advice you were given by professionals who are also humans. Everyone can make mistakes.

I've seen kids around the 10-12 months too...a lot of this started with the back to sleep campaign.  Back when I had my kids, it had just started, and though it can save lives, it can cause other issues as you well know.

In my case I used one of those side sleepers and during naps it was on their stomachs but I would be awake to monitor....I never fully obeyed the  back only-because of this reason.  

Listen, mom guilt is a real thing, just discard that, it won't help you or her at this point, honestly I'm surprised they didn't recommend the helmet earlier or found away around the insurance issue for you.  She's not 'too old' to start it now though. 

But wanted to respond since I have been there and you should NOT feel guilty!  You were following the medical advice, which unfortunately is often contradictory. And at 6 months your DD should be young enough that even if you go with the helmet it should work, I think. We were in a similar situation when my BS was about 10 months. Pediatrician referred us for a consult, one neurologist said maybe. I moved heaven and earth to get an appt with another highly regarded neurologist at the area children's hospital who said, this kid needs a helmet yesterday! And I freaked out, found all sorts of internet research and found the absolute best helmet place (a 2hour drive away who did not take my insurance). I was fully prepared to plunk down the $ and fight it later for the sake of my kid. I was also worried that the older he got, the less it would work and the more difficult it would be since he would figure out the latch pretty quick. But turns outs, the helmet place refused to take my money. Said it was unnecessary based on DS's head measurements. IIRC, the difference between the front to back head measurements on either sides of the head are supposed to be 3 mm or less. DS's was 4 I think. They basically said don't worry about it, he'd be fine. And 10+ years later, he is. So this is a long winded way to say doctors are not always right. They will disagree. It is not your fault. You will figure out the answer that works for you. For me, it gave me a bit more faith in humanity that the helmet place would not sell me something ( at great profit to them, I am sure) that was not necessary. 

Wow not sure how we all survived as infants sleeping on our tummy etc.  My son slept on his tummy and my granddaughter will roll over in her sleep to her tummy.  I think a lot of these modern parenting edicts are faddish and bubble boyesque.

Don't beat yourself up.  See what you can do to obtain the helmet if possible and call it a research phase.

Ugh! This is a prime example of doctors not being helpful. If I were your daughter's primary GP, I'd be livid at my colleague for undermining my result. It would be one thing if you had asked for a second opinion, but for another doctor to seek you out to give contradictory advice. What would be the harm to your daughter of having a helmet? I see lots of babies with helmets these days, so it's more common than many doctors like to let on. That second doctor should not have put you in the middle of a conflict she has with a colleague. 

One of the things that surprised me so much about becoming a mom was the sheer level of mom guilt...the guilt you feel naturally and then the guilt that society tosses on to you. It's not fair. The first doctor should not have said to you that he was concerned about the effectiveness at this point..again, he's putting you in the middle of the conflict with his colleague. Unfortunately, I do not have experience with helmets or docbands, but just remember you are doing your best and making the best decisions you can with the information you have. 

I can't say that I've had a child that has this but my son (now 10) was born with Severe developmental delays.  We have had early intervention with PT, OT, ST and a nutritionist at one point(he now has an IEP and does OT, ST-and a diagnosis of auditory processing disorder).  The poor kiddo split his chin open the first day of PT because he didn't know to brace himself when he fell.  No one knows why he was born like this nor did we have an actual diagnosis.  Many times I've had guilt about things I did during pregnancy that 'could' have made him this way (nothing big-just being hard on myself) I still wonder if getting pregnant with an IUD in place affected him..no one will ever know.  Don't be hard on yourself, if you are doing what you were advised then you are doing your job momma.  Stay positive, your kiddo is lucky to have you.

A lot of the flatness corrects itself at the 6 month mark when they roll over and spent time on their tummies. If you can, carry DD around with you in a chest harness. And time off from laying flat on the back of her head should help. 

I don't know anything about helmets and such, but I do know you are a good mother. I can tell not only by how you talk about DD, but by the concern you show for your SS. This will all work itself out. You were acting in her best interest based on the medical advice you were given at the time. You now have new information, and you are acting on it. Don't beat yourself up. You are doing your best, and both DD and SS are lucky to have you!