I've already posted here a few times about my MC, but a v brief recap - ttc for DC#1 for 18 months, MMC at 10 weeks (6 week embryo), completed naturally last week.
Less than a week before we discovered our MMC we found out my SIL, who lives locally, was also expecting DC#2 with an EDD just over a week after mine. Obviously there was much mutual elation at that point.
Since the MC I have obviously generally been a bit holed up anyway, but have specifically avoided all contact with BIL and SIL because, while they've offered sympathy and been very kind, I just cannot cope with the fact she's about to go public with her news and will reach all her pregnancy milestones when I should have.
DH has been in touch with them but I just can't bring myself to do it even though I want to try to ensure there's no rift or anything because I am still happy for them and their pregnancy. I just had a nice text from her saying she's thinking of me etc. but I'd feel like a fraud replying saying thanks etc. when I don't know that I can actually face seeing her, at least without explaining.
Christmas is going to be a nightmare too. MIL also lives locally so we usually do a belated Christmas meal with her and BIL/SIL and my niece but I don't know yet whether I'm going to be able to cope with that. 
Help! Does anyone have any advice on how to explain to my SIL that I'm not being a jealous bitter bitch, it's just that my emotions are not reliable and I don't know how long that might last for?