Where can I take her to hang out?

I am in love with my bestfriend but I'm also close friends with her Sid at around the same time we met but Iv always had feeling for my bestie. Iv once asked her if she wanted me to buy her a coffee and she thought it was sweet but she had to go downtown for something important so she said she doesn't think we will have anytime. Two weeks later I asked her if she wants to get some breakfast with me. She said "aww thank you but it's ok" she probably said that because before I asked her what she was doing she was going to work for her shift. We have been seeing each other alot lately when I visit her and she's showing more affection towards me than usual. She and I always were attracted to each other but never acted upon it but since we have been seeing each other alot more often and acting sweet towards me I feel like I have a chance with her if something doesn't come up. Where are some places we could hang out because I was thinking of asking her to get some lunch with me or we could go to the mall and see a movie if she wants..I'll buy of course. Btw what is also making this more difficult is that her sister and I are also close and I will feel kinda bad if I don't include her but I want to be alone with my bestie.