Hi, OP. The recent resurgence of popularity for Interview With A Vampire is because of a tv adaptation. It's on iPlayer if you want to have a look. The unique selling point of this adaptation is that it takes the homoerotic undertones of the book and makes them more upfront. It's Louis and Lestat in a gay relationship, basically, complete with sex scenes.
I mention this because it seems unlikely your teenage daughter, who spends a lot of time online, didn't get into the book through the show. It's a pretty explicit show. Think Game of Thrones or True Blood. I doubt it's the kind of thing you'd allow your fourteen year old to watch normally, so if she is watching it, she's streaming it behind your back. That's one point to consider.
Another point is that the way you describe her . . . if she is a big fan of this show, there's no way she's not involved in online fandom for it. She will hide this and delete any history if she knows you're looking, but she will be spending a lot of time on Tiktok, Tumblr, and the fanfiction writing site Archive of our Own (AO3 for short.)
Let me be very clear. You might think this is cute and harmless - just teenage girls writing stories about the male characters they have a crush on. But the vast, vast, vast majority of what she's reading will be explicit gay sex. Far more in-depth stuff than she's seeing on the TV show. Less than one percent of fanfiction is what you might call "gen fic" (stories about the characters). The rest is romance stories with a lot of explicit sex scenes, or just straight up porn. Anal sex, anal fingering, rimming, and things like that, will be standard fare in almost every story she's reading. Given that it's a vampire fandom, I can tell you without even bothering to look that there will also be a heavy presence of kink. Blood-drinking, choking, and BDSM are a guarantee.
This is your daughter's first exposure to sex. Everything I described will be completely normalised within the fandom. Young women like your daughter - every one of whom will describe herself as having ADHD, autism and anxiety - will be the ones writing these stories. She'll think she's found her people.
In this community, "kink-shaming" is considered a form of bigotry akin to homophobia, so no-one will be reining anyone else in when they go too far. No-one will want to be mean and tell them the kink stuff is ridiculous. Or admit it makes them uncomfortable. As you can imagine, this leads to the autistic, inexperienced young authors diving deeper and deeper into kink to gain clout with their peers. It makes them look more mature and gets them respect if their fics are more sexually explicit. Everyone's chasing novelty. It's not uncommon for girls like this to freely admit to watching gay porn to get "inspiration".
The boundary is getting pushed further and further out, and the younger people coming into these fan spaces have no reference point for what's normal. So they decide it all is. They form the opinion that extreme kink is just sex, and think it's what is going to be expected of them in adulthood. You can imagine the issues these girls are developing as a result.
If your daughter is clinging to toddler things the way you describe, two things could be happening. One is that she's regressing out of fear. Adulthood is sex and sex is scary and degrading, so she wants to go back to being a little kid. The other, more disturbing option is that she has encountered a kink popular in these spaces, known as "ddlg" or "daddy dom little girl". Basically one person infantilises themselves by behaving like an actual child, and then another comes along and "doms" them (in the BDSM sense) by being their sexual "daddy".
I'm sorry. It's as vomit-inducing as it sounds. But you will see young girls caught up in this on these social media sites. Live streaming with strange men from their bedrooms. I don't mean to scare you, and I hope this isn't what's going on with your daughter, OP. I don't think it's likely.
But I do think she has probably been exposed to sexual content she wasn't mature enough to cope with, and she's struggling to process it. I think there's a side to her you're not seeing, and it would be a good idea to check her devices.
Plenty of autistic teenagers have a plushie collection, but for a fourteen year old to be watching In The Night Garden at the same time as reading Russian literature, is unusual.