Is this just picky eating or ARFID?

I have a stepdaughter, 5, who is very selective with her eating. One of the first things her dad ever told me about was feeding struggles when SD was a baby. She would scream and wail for milk, but when offered, would refuse to drink. She wasn't meeting growth milestones, but the doctors had no answers. She went to every specialist, even having an endoscopy at 2 years old. When she graduated to solids, she began eating more and is now gaining weight and growing.

Obviously, I was not around during this time frame as her parents were still married. It sounds very traumatic of course and I can't imagine what her parents were going through trying to figure out what was wrong, and coming up with no answers.

However, bringing us up to present moment, SD is a picky eater. Her "meals" aren't really meals- it's a variety of snack-type food, such as "meat sticks" (essentially slim jims) cheese, peanut butter sandwiches, all types of fruits, carrots, broccoli. The only real meal she'll reliably eat is a hamburger.

I cook family dinner every night she stays with us, so I always give her a small plate of our real food alongside her usual dinner. A couple of times we've gotten her to try something new- and every. single. time. she immediately spits it out and goes "blech" without having even chewed it or hardly tasted it. We still tell her good job anyway, and we aren't forcing it whatsoever so on the rare occasion she tries something it's purely her own decision.

However, we're starting to run into some problems with her usual foods too. I get her grapes for breakfast, she doesn't want to eat them because she only likes the skin on "half the grape." Translation- she wanted me to cut her grapes in half. I wasn't about to concede to this, as she's perfectly capable of eating a whole grape, so I told her if she wants them cut in half she can do it with her teeth (lol). I go to grab her dad for backup, and by the time we get back in the kitchen she's eating the grapes and says she changed her mind, she doesn't want them cut in half.

That same day, she gets home from school I'm unpacking her lunchbox and she's hardly eaten anything. We pack the same things every day- meatstick, cheese stick, carrots, some type of fruit. I asked her why she didn't eat lunch today, and she told me she didn't like the cheese because it was an old package and she only likes new cheese. I go to the fridge, pull out the brand new package I bought the day before, and show her the cheese in her lunch was literally the first cheese stick pulled out of the brand new package. She goes "Oh! Ok, you can pack that tomorrow" ?????

These are just the most recent examples of her particulars about eating. Her dad's convinced she's got some sort of eating disorder based on her feeding struggles as a baby, and we need to just be happy with the food she will consume. I'm of course on board with letting her eat whatever will fill her up, but I think we need to start being more firm about expanding her diet as well.

I've been reading more about ARFID in children, but I don't really think the symptoms I'm reading about align with her. She does have certain "safe" foods but they're a wide variety of flavors and textures. She doesn't fear choking. She does get afraid to try something new because she's scared she won't like it, but that's also pretty textbook to plain old picky eating.

I'm curious about people's childhood experiences. Please weigh in if you have been diagnosed by a medical professional with ARFID. Can you relate to my SD's food habits? Were there certain things your parents did that helped you eat more, or things they did that caused you to be more avoidant? Thanks for reading and any advice!