Need advice? Touchy subject? Kinda long...

My SIL who is also my best friend she found out she was pregnant & told everyone as soon as they found out I found out 4 days later I was pregnant but have decided not to say anything yet to anyone she went for her 8 wk scan and they couldn't find baby everything was there for a baby but the baby :( a week ago my SIL misscarried I was there for the whole thing it was very sad and I feel So bad for her! I just went for my 8w ultrasound and heard babies heartbeat :) baby is measuring exactly where baby should be this would of been both our first kids and we also talked about getting pregnant together (not that we ever thought it would really happen) We also just found out that are other SIL is pregnant also. We all would of been  1 week apart! I still have not told anyone as I feel she needs to be the first... My question is how do I tell her without hurting her? I don't want anything to come between us I want to tell her alone so she doesn't have to feel that she has to be excited for me or put on a fake smile!  My other SIL kinda rubs it in her face & I wouldn't ever want to do that to her but I also feel bad because I feel like I'm lieing to her by keeping it a secret this long?? Any advice would be greatly appricated! This is my first baby & I want to be excited but this just weighs so heavy on my mind!