My main character slips into the world of a book she is reading, where she interacts with a character from her favorite book. Does anyone have any advice on how to make it clear when switching from the main character just reading the book to what is actually happening in her life? I've heard of using italics (which wouldn't work well in my case since I'm using italics for thoughts.) The other method I've heard of is using a different typeface for when she is reading the book. Thanks in advance for any suggestions!
Don't resort to formatting gimmicks (I would include italics for thoughts in that, but that's another 500-page thread). We're authors - our job is to convey things through words. Wouldn't you have some kind of transition where the world around her changes, or the character materialises in front of your character? Describe it, and then the reader knows what's happening.
is she "interacting" like she's talking to the character and her imaginary world and real world bleed together? or are we just talking about her reading a book and having another story playing out through her eyes? i would also ask what purpose having her read a book serves. is she escaping an abusive relationship, doing assigned reading for school, exploring an old journal she found in the attic, etc? how is this window in to her reading moving the story forward? for example, if she's reading to escape we might be focusing more on the indulgent qualities of this book that offer her comfort and a sense of control. if she's reading an old journal by say, a distant relative, then there's a greater sense of curiosity and overarching questions about what your MC is going to find out. i feel like answering these questions may lead you in a better direction to answer your original question because each scenario may be approached differently.
If the book inside your book is stylistically different enough, your reader should be able to differentiate between the two "worlds". When I say stylistically, I mean in terms of tone, wording, etc. The portions of the text are not physically different (ex. alternative font).
Watch Neverending Story. It's an 80's movie with this same premise it will give you an excellent idea on what to do and what not to do. (In the sense of showing)