SIL infertility

My sister in law has been battling with infertility for approximately a year and a half and his about to start IVF in the next few weeks. However, for the past year she has been openly angry towards her family and friends. I know it is from being sad and grieving about infertility but it is making a big rift in our family with how ugly she is towards them ( ex. makes disgusted faces at cousins kids, snarls, rolls her eyes when her grandma tries to even speak to her, etc) . Anytime that someone tries to speak to her about her anger (in a loving way non confrontational way) she says that we don’t know how she feels and just writes them off and is done with them. I often feel like I am the liaison between her and the family and trying to keep the peace and is empathetic between both sides, because I know she is hurting but it’s no excuse how rude she is to all of her loved ones. However, I know with the holidays coming up along with her IVF treatment, I know that family events are going to be even more tense and palpable than usual. I don’t know what to do..... I honestly want to talk to her because I believe that she is depressed and needs counseling and medication but I am afraid that she will close me out too and I don’t want that to happen during her IVF treatment. Any advise? My heart is aching