You can't disagree with your pushy mother-in-law -- it's her way or the highway. She complained that you're not feeding your family right and showed up to prepare their meals. After you changed the front door lock so she couldn't keep dropping by, she barged in through the back door. When you asked her to stop spoiling your preschooler, she bought him a new video game. She even pushed her way into the delivery room when you were giving birth and posted the video on her Facebook page. It's time to let the meddler know who's in charge.
Enforce strict boundaries. Stop allowing her pushy behavior by drawing your own line in the sand. The next time she barges into your home without calling first, let her know it's an inconvenient time and politely show her the door. Inform her that in the future, you'd appreciate it if she calls before dropping by. If she continues to ignore your request, ignore the doorbell. When she pushes advice onto you, say "Thank you for caring, but I prefer to do it my way." If she constantly phones at all hours, stop answering or allow voice mail to take the calls.
Behave as your bossy mother-in-law's equal, not her child. Let go of your need for her approval. By giving her power to override your own parenting decisions and do things her way, you're allowing her to infantilize you. Show her that you're the parent and fully capable of making responsible decisions by stopping her in her meddling tracks. The next time she pushes an unsolicited piece of advice onto you or oversteps a boundary, calmly say, "Thanks for your advice, but I've decided to do it my way." If she argues, say "The subject isn't open for discussion." You don't need to defend yourself or offer any explanation for your choices.
Work with your husband as a team and confront your meddlesome mother-in-law together. Don't insult your mother-in-law to your son, or list for him all her bossy traits, which could cause him pain. Instead, the two of you should have a polite but honest discussion with her, informing her of your concerns. Since he's her son, he should initiate the conversation. Be respectful but firm. Begin by saying, "We know that you mean well, but please stop buying our toddler toys behind our backs." Or, "We appreciate your help, but we don't need you to cook our meals."
Be prepared for her to possibly act out after you begin drawing healthy boundaries. Don't allow her to manipulate you with guilt into reverting back to placing her needs before your own. She may play the victim by crying, hurling insults, making threats, accusing you of being a bad mother or not caring about her opinions. Stand your ground. Don't react by becoming equally as insulting. Remain calm and say, "I'm sorry you're upset, but this isn't up for negotiation." If she continues to push, say "This conversation is closed."