Am I under any obligation to speak to her?

My husband and I are seperated and most likely divoricing. My mother in law calls me multiple times a day and if I dont' answer her she leaves me nasty messages. My husband and I have one child and my mother in law says that she just wants to know how her granddaughter is doing, keep in mind she has never done this before until we decided seperate and she only sees her about once a month if that, and she only lives 15 min away. Anyway, I feel if she truely wants to know how her granddaughter is she can call her son(my husband) and ask him. Not to mention that when all this happend she told me that it would be very sad if we ended up getting divoriced and then told my husband that divoricing me is the best thing to ever happen to him because I am crazy and he could do better then me. Well thank you in advance for the answers.