Two weeks is plenty of time to get your house guest-ready. Breathe.
1. Where is she sleeping? Get that area ready first and give her room to have a suitcase and hang her clothes and shower, etc.
2. What will y'all be doing while she is here? Plan those things, even if loosely, and create space in the house, if needed. For example, if you want to go places, start looking for where and how to get reduced prices. If you plan to just hang out with the baby, then get the rooms ready where the baby spends most of his/her time.
3. If you don't already have routines in place to keep the kitchen clean, develop some and practice in the next two weeks.
4. Walk up to your house as if you were a stranger. Straighten along the way (pull weeds, put away items you don't even see anymore, etc). Clean the door and walkway.
5. Walk inside your house the way you'll be doing it with MIL during her stay. Is there room for all of you? Clear the space, clean a little, add a welcoming touch. Develop a routine to keep the entrance clear and user-friendly.
6. Spend your remaining time on areas where you'll be spending most of your time during her visit.
Meanwhile, the only way your house is going to stay clean after MIL leaves is if you develop the routines necessary to keep it that way. Defining your level of comfort and what "clean" means to you may be a worthy endeavor...