Everybody develops at different rates. Some babies get their teeth early (my son started getting his at 5 months) while others get them later (my daughter started getting hers at 11.5 months)... same with walking, talking, etc.
There's nothing wrong with your daughter not walking, unless, of course, there IS something wrong, but if your doctor thinks she's okay, she probably is. My son refused to crawl - he just liked to lounge and stand around hanging onto coffee tables and furniture
And then one day, he started walking and he was over a year.
If you can't move out, I suggest you tune your MIL out and read up on child development, either online or through books at the library. Maybe attend some mom and tot things on the weekends and get to know some other moms of young kids. You'd be amazed at the wonderful friendships you make, and the support you can get from other moms. Some of them may be experiencing the same things you are. If you really are concerned, though, ask your family doctor about this.
And don't let her get to you. She is what she is and you're never going to change that. All you can change is your
attitude, so try not to care. Like as not, if she didn't pick on this, she'd find something else. Think about whether she's like this as a rule or is she just picking on your child.
When kids are 20, nobody remembers or cares when they began to walk and talk, etc. but they all managed to do it. It all works out in the end.
Good luck, and keep us posted.