L.R.
Please get her to an occupational therapist (one who specializes in young kids) for immediate evaluation. She may have a sensory processing issue, as others said, or she may be like my friend's son, who needs to chew to focus his mind on any task.
She needs evaluation and help now, because from what you describe she is at a high risk of choking!
She needs safe items for chewing, and those are available, but you need an OT to work with you on what items to use and how to make them available to her. Don't go it alone and just buy her "chewies" -- get her help as well. This is something other families experience too, so you are not alone.