Is it normal that she does this to me?

I've heard of rape or sexual abuse of as a man forcing a woman for sexual activities. My case is the opposite.
Me an my sister grew up as very close friends, hanging out, going to the gym and even talking about sex. She is 2 years older than me and she has always considered me her best friend even though I am her little brother. The other day after we got out of the gym I gave her a ride to her house cause her car was at the mechanic shop and she asked me if could hang out with her at her swimming pool since she needed some company because she just broke up with her boyfriend. I stayed and went swimming with her. We drank a beer and talked while getting some sun on the beach-chairs. She told me that her ex-bf used to hit her sometimes when he got upset. I got up hugged her and kissed her on the check and told her she was alright now. She started to kiss me and grab my penis, I was surprised! Then she pulled my shorts down, grabbed my buttocks and started pushing my penis in her mouth, I was in shock! She pushed me down on the beach-chair, moved her bikini bottom to the side and pushed herself on my penis. I made an effort to stand up from the chair but she just held me down with her body weight and put her breasts in my face. She kept rubbing herself on me until she orgasmed which made me cum inside her. Afterwards we just stayed there inside each other holding each other. She told me she's always loved me and has been very attracted to me. I told her I was worried specially since I came inside her and she told me she was on the pill. I thought this was just a one time thing but it has happened 5 times already and she always instigates it by grabbing me and taking our clothes off.