The singer and actress admitted that she is "shy" because she did not attend school often enough.
She told The Guardian: "I don't really have many friends. I never have. I was always a loner. I was in and out of school so much - so, I dunno, I'm really shy.
"Which is weird because you probably wouldn't think that. I've got my six best friends, and three of them are on tour with me the whole time so that's awesome. It's not sad or anything for me. I like that."
Momsen, who turned 17 earlier this year, added that her birthday was made special with the dessert she enjoyed.
She explained: "We had cake, although I don't like cake. I like brownies. But actual cake? I dunno. Something about it, too cliché.
"I was in Paris and they do shots of espresso over ice cream. Oh my god, that was my favourite thing ever."