I think the first port of call is the old chestnut- put yourself in the other persons shoes. You know, dont gush and dont go into to much detail about your own happy circumstance. But most of all just be sensitive and take ques, read her and offer support. Its easier to be happy for someone who shows empathy than someone who just, in the eyes of the recrently beareved, 'rubs the pg in your face/ wounds'.
Dont expect too much and be open to the persons non-engagment with your pg. It doesnt mean they dont care or are not happy for you- they are grieving, and seeing someone pg could very much make them feel sad, inadequate and remind them of their loss.
Tread softly and ask....find out how they're feeling or as the case might be..how much they do or dont want to speak about it. Be careful what you say..dont say silly things ( im not saying you would, but some things can be very hurtful when you've just had a mc)
I'd probably appreciate a nod to my loss..such as ' i do not want to upset you as i know you are going through a very tough time, but you are important to me and as such i would like you to know that i am pregnant.' It might go down well... or it might not..again its not you but the bereavement and grief you are seeing so dont take it personally.
At the end of the day everyone handles this differently, but if you want to make it easy for her let her choose the amount of involvement with you and the pg.
I dont think you will find anyone who has ever had a mc goes around showing their envy. In fact most of us feel terrible guilty, more than you could know short of this actually happening to you. Trust me you will never know. But as i said above, she might choose to disengage in baby showers etc etc. It could just be too painful!! Or you could find she finds this an outlet..or more likely..puts on a brave face. Dont let her!!! Be a friend and let her do what comes natural to her!
Sorry for your friend/family's loss and congrats on yout bfp's!
