First call my daughter and tell her to find a hiding place...out of the way...in a corner, make herself as "little and quite" as possible. Next call to the police...inform them. Does this Walgreen have a drive up? If so I would make my way to them and inform them. I don't think I would bust in. I would probably draw my weapon and station behind some cover as close to the front door as possible without being seen by the BG. If you could go in a back door...that might work, but being a drug store...I doubt if you could. Actions after that would be dictated by the actions of the BG.