Could this be depression?

I've been worried about my friend recently, her mum died about 3 months ago from pancreatic cancer. Ever since, shes never quite been the same, I know she's not exactly going to get over it quickly but I'm starting to get really worried about her. She's lost her appetite and her weight has dropped quite a lot, she's normally quite tearful nowadays and has quit most of the clubs she used to do before. Her grades are a ton worse now, its like she doesnt care anymore. She doesn't want to hang out anymore at weekends or afterschool, she prefers to be alone, I know she's not sleeping well at the moment and she can't seem to concentrate anymore. Is this just her grieving or is it something worse?