dont over think it. take her out for something you both enjoy doing. get her favorite food. and just have a good time. and then let her know how you feel. dont be overly expressive. just talk to her how you normally would. and tell her its alright if shes uncomfortable with moving in a different direction because regardless you like the way things are now.
my basic advice would to just take her away from w.e shes doing and just ask if not do what i said earlier if u really are friends she wont like not be ur friend if u asked her out and she didnt want to