Does anyone have ideas for activities to get my mom out of the house?

Depending upon her situation (see JeanneGibbs question) just about anything can be fun. A little league game in the park, a movie, a middle or high school theater production or concert, a trip to the grocery store or one of the 'marts', a service or talk at a house of worship, a volunteer stint at a non profit (our food bank has seniors do the folding and stamping of newsletters and appeal letters so they can sit for the time frame, programs at the library --- ours shows a movie each week, a trip to an ice cream store, the list goes on and on. The most simple things can get someone who is alone excited.

We took our Mom to the museum today. She can't stand very long, so we had a transport wheelchair for her, and it worked perfectly! We went to the California Science Center in Los Angeles, where the Space Shuttle Endeaver is, and she just loved it! My Dad was a chemist, and developed the coatings for the heat shield for the Geminii flights, so it was really cool to be able to get under the wing of the Endeaver and look up at those heat tiles and know that my Dad had something to do with it.

I think Art or Natural History museums can still be attractive to most elders, and in nice weather, take them to a rose garden or botanical park if they were into gardening. Many elders liked to do crafty type things, and while they can't do that any longer, they might appreciate street fairs where vendors show off their own crafts. Again, wheelchairs are a big asset - sooo glad we got that for Mom. A whole new world has opened up now, and it was only about $150. Well worth the money!

Unless you're on a tight budget, give her $30 every now and then. ... $20 to buy some staples and $10 for her; as an incentive to move and socialize. She might go get a banana split just for the heck of it and spend your $20 on something else, but it's a start.

I'm not making light of your situation, but sounds like she needs to regain a sense of purpose. And without something useful to do, that's not going to happen.

What are Mom's impairments? What are her interests?