It sounds tough my friend. If your mother in law has been denied 3 times, do you know why? Is her record with US immigration clean? (i.e., has she been deported?) If so, she might need to file for forgiveness (I know it sounds arrogant but there is really a form for that) at a US Consulate or Embassy in her country of origin. Once her record is clean (takes about a year) she will be able to apply for a visitor's visa again. Then, make sure the documents she brings in her application show enough evidence that she will not stay in the US (i.e., her job, business, property, etc.). Good luck with everything and congratulations on your baby.