Autistic teen and diet/constipation issues

[Utterlypeanuterly]

My 17 year old dd is currently being assessed for autism and it looks very likely she will be diagnosed. She has suffered with anxiety in the past.
She's had sensory processing issues since she was a toddler and part of this is that she has issues with food.
She suffered with constipation as a child and was on Movicol.
She has become more and more restrictive with the foods she will eat to the extent that she doesn't eat any fruit other than bananas and no vegetable other than potatoes although she goes through phases where she will eat vegetable soup if it is blended and lump free. She loves carbs and eats meat.
She is incredibly bloated all the time and I know that she is quite badly constipated although she hates discussing it. She won't go to the doctor or try any of the things suggested by the pharmacist.
A close family member died recently due to complications of a ruptured bowel. It was horrific and I am now constantly worried about dd. I don't want to scare her but she doesn't seem to understand how serious it could be. Even if it is nowhere near that stage she is so bloated and uncomfortable and often feels quite sick.
Has anyone any advice on how to help her understand or hoe to proceed?
She is nearly an adult so it is difficult to know what I can do if she won't help herself.

How is she with drinking water? Sorry, maybe a small issue but it was my first thought: if she’s willing, I would up the water intake.
My teen is recently diagnosed ASD and has always had ARFID. Sounds very similar to your DD. However, my DD doesn’t eat any fruit or veg at all. Mainly cheese and chocolate 😩 Luckily for her no constipation. However, she’s actually enjoying tracking her water intake just now in a new diary. Maybe a ritual like that would appeal to your DD?

Will she drink fruit juices. I was recommended orange juice by a pharmacist when ds2 had constipation issues (probably from eating too much cereal and bread). And as poster above says making sure she drinks enough in general helps.

I can’t really offer advice, only support as my 16yo dd is exactly the same. Staple diet of cheese, pasta, baked beans and the occasional jacket potato (with butter and cheese). No fruit at all and only sweetcorn for veg. At my wits end trying to get her to try stuff!! Only drinks milk and occasionally water.

Thanks everyone.
She rarely drinks water. She drinks a lot of tea. She had been looking quite pale lately and I know too much tea impacts on iron levels.
I think this summer has really shown up the issues. She had a job for the first few weeks but she wasn't able to find something else once that ended. She refuses to do a single thing to help herself.
She will drink orange juice, eat yoghurt and berries and some other healthy things but only if I constantly prompt and remind her. Otherwise it's tea and toast or potato waffles.
She is almost an adult. I took a step back this summer to see how she would manage but she made no progress in looking after herself at all.

You mentioned bloating and to me that screams food intolerance. I am gluten and dairy intolerant, both cause bloating. However gluten causes mild bloating but long list of other symptoms (many are severe and turn me into none functioning vegetable). Diary causes extreme bloating and some very mild other symptoms but in long run those mild symptoms caused quite serious life changing health problems.

I only last year figured out I am autistic (at age of 43)😵‍💫