My sister wont let me talk to the girl I like

well I like this girl( im a girl too ) and she likes me too. I wanna ask her out and I told her too. theres only one problem, shes my sistres friend and she doesnt even want me to them. She caught me talking to her once on facebook and she made the both of us promise to never talk to each other again. we still talk but secretly. she doesnt wanna lose her as a friend and I dont want her to hate me cuz im her sister. she told me she loved me yesterday and I really wanna be with her but I dont kno what to do about my sister. I really need someone to help figure out wat to do. and I kno some ppl might say that it shouldnt matter what she says but trust me shes a way different sister then most. soo plzz help .

What would happen if you and the girl sat down with your sister and said you understand how she feels and will do you best to be sensitive to those feelings, but you'd also like to ask her to be sensitive to the way the two of you feel about each other and would like her support...?