My MIL is bored and always wanting to intrude...

I feel horrible saying this and I love my MIL but she's bored and lonely and always wants to tag along with things I'm doing. When I take my son to mommy and me classes it's akward because it's a bonding time for me and my son or me and the other moms (we often joke about our husbands).

I told my husband about it but he's siding with her and thinks I'm being rude when I decline. I don't know what to do. She asks to hang out nearly every day.

Edit: Her husband (my FIL) owns his own business and makes enough money that she doesn't have to work so she's home all day with nothing to do besides housework and unfortunately often day drinking if she's not with me. She's been like this as long as I've known her, which has been 10+ years.