Hello, that's great she's getting into reading, you must be so proud! Some great suggestions already. My thoughts - I will say, they span a lot of styles, topics and levels of difficulty, but so they should, any learner needs variety. She mustn't pigeonhole herself as a lower ability reader. If something is challenging, great! The sky doesn't fall in if she doesn't know a word, it's a learning opportunity. Equally, there's nothing wrong with reading something she finds easy, ie can read fluently right away, but enjoys.
Firstly, does she / would she read comics or magazines? If your goal is to get her reading regularly, I would really recommend this. There are also online magazines and blogs of course, but there's something about physically holding a paper magazine.
From there, might non-fiction books work? This might get her to realise that reading is useful and interesting in the real world. Also, many are so well-structured with short sections within sections, text boxes, photos and diagrams - it's a great way to get reading. I don't know what her interests are but there will pretty much a 'For Dummies' book for her, whether it's fashion and beauty, health, cookbooks, how to care for your gerbil or play the ukulele, history, travel guides, travel memoirs of reporting from war zones or sailing around the world. Even celeb 'biographies' would work if she's interested. Then there are always teenage life guides, I loved this, and suspect that despite the Internet etc, the themes of teenage life haven't changed all that much: www.amazon.co.uk/Thirteensomething-Jane-Goldman/dp/185340246X?tag=mumsnetforum-21
Teen fiction is always a winner. Judy Blume's 'Are You There God? It's Me, Margaret' is perfect, aimed at girls her age - (almost) anything else by her is good, too. Lois Lowry and Paula Danziger are also good. Then continuing the nostalgia trip of what I read at that age there are the Babysitters Club and Sweet Valley Twins series. Short, easy to read, lots of them. For something more modern along these lines, the Pretty Little Liars series (the TV series is based on these).
The original Diary of Adrian Mole aged 13 3/4 might work, more accessible than it may sound, very funny, and again, the themes of teenage life haven't really changed all that much.
If she's seen and liked a film that might be motivating - The Fault in Our Stars, My Sister's Keeper ('adult' book but in short chapters written from the point of view of each of the main characters in their own style, so quite engaging), The Perks of Being a Wallflower, The Girl With all The Gifts, The Hunger Games, and of course Harry Potter (obviously earlier books for now).
Philip Pullman's Sally Lockhart series, if she's into history/ crime, grabbed me at a little younger than her.
A Series of Unfortunate Events series, I love it, quirky, short, hilarious. Or how about anything by Terry Pratchett, for fantasy/ supernatural, or Darren Shan's Cirque du Freak series www.darrenshan.com/books/listing/the-saga-of-darren-shan
Some good ideas here: www.theguardian.com/childrens-books-site/2015/jan/22/top-10-books-for-reluctant-and-dyslexic-readers
www.understood.org/en/school-learning/learning-at-home/encouraging-reading-writing/ and here, although more aimed at older teens.
Finally, I recently enjoyed this www.goodreads.com/book/show/34382011-see-how-they-lie as an educated adult, it kept me turning the pages, but is also aimed at teens and very accessible, fast paced, with simple language. Really recommend. If this appeals, she's written other books.
Wishing you and your DD much enjoyment.