One option would be having your MIL / wife join Mom's Club of Irvine. The whole point is to get young children and their stay-at-home moms / families together for interaction and support. They have weekly play dates at the park - usually one weekday morning around 10. Then they have a bunch of other optional activities thrown into the mix whether it's a holiday party, a charity drive, a field trip, etc. They even have a mom's night where the moms get together on their own once per month. Since your wife doesn't have regular coworkers, she might like that opportunity to know more moms in the area. The cost is a negligible fee per year. I did this type of club for five years. It was a very good experience.
This way, baby gets to play with other kids, plus you don't have a big monthly cash outlay, and mom / grandma get to form bonds of their own with neighbor families.
Here is a list of M.C. Chapters. It has 5 listed for Irvine. If you don't see your area listed, you should contact Moms' Club. Sometimes there will be chapters that are newly formed and haven't been added to the roster yet.
http://www.momsclub.org/links.html#California