I'd suggest that you apologize only for not handling the situation with grace. Don't apologize for telling them what you need.
Complex family issues usually call for establishing clear boundaries, understanding our own legitimate needs, and balancing them with others' needs. None of this comes easily, and is a life-long effort for many of us. Fortunately, once we see the need for clarity, there are communication techniques that can help us get there. There's an approach called Non-Violent Communication (NVC) that I have found extremely helpful in a number of relationships, including with my husband. You might wish to experiment with the process. Here's a brief outline of the steps, and simple examples:
1. Say what you observe happening, in clear, non-judgemental language. "I notice that you come here to be of help, but lately I have more and more work to do in order to host your visits."
Be really, really careful at this stage to keep your observations free of emotional language, like "You're taking me for granted," of "You act as though this is your home and I'm your maid." Even if they feel true for you, statements like those will poison the possibility of meaningful progress.
2. Make a stab at what her motives might be. Use the most compassionate language you can. "It seems that you feel like a regular part of the household now." Or, "I can't help but wonder if you see these visits as mini-vacations for your family?"
3. Tell clearly how you feel about it (not "you MAKE me feel negative," but rather, "when you leave all the meal prep and housekeeping for me, I FEEL some negative emotion." A fine distinction, but empowering). Or, "I feel angry / hurt / upset when you assume I will cook for you during extended visits." Or, "I notice I just feel stressed and exhausted when we're expecting another long visit from all of you."
4. Tell what needs you have that are being violated or ignored. "I need more privacy, more time to enjoy my family, and less work." Or, "I really need you to consider my feelings / needs / wishes here." Or, "I so wish I could relax and not dread your visits."
5. Make a clear request that is within the other person's ability to satisfy. "So, I really need for you plan shorter visits (and/or bring fewer people, and/or participate more in the work your visits involve)."
This approach will help establish grownup boundaries, while respecting both your in-laws and yourself. Obviously, you can combine the steps above into a more natural flow, but I've separated them for clarity. Learn more about this approach by googling "Non-Violent Communication." There are books, examples, workshops, and local support groups if you find it helpful.