Hi S.,
I too am going through the same thing you are doing, I have a 2 year old and 5 month old. When my 2 year old is here she takes a 2 hour nap around noon w/ no fussing. At my MIL's house, she fights and cries. Reason is she set the tone for her, she puts her down, 2yo cries and she gets picked up. Here, it's all business, I put her down, she sleeps, end of story! It's been an ongoing struggle since day one to force her to put 2yo down, the reason is she does not like to hear her cry! Well, I don't like her to be a fussy mess when she gets home so my husband and I began doing this about 2 weeks ago (tough love for MIL). He usually gets off around 2pm, gets to her house around 2:30 - 2:40, if she was to put her down this would be more than enough time. She doesn't, so he stays there w/ her until 5 or 6 (i'm at work) saying that he wants to wait for traffic to die down. See, she sends her home not knowing just how awful she is, we live about 30 mis away from my MIL, 2 yo usually falls asleep in the car on the way home and is very upset when she's awakened. Since he's been staying there she has a chance to see just how grumpy 2yo is with no naps, I think this really helped her put it all togther. However, you HAVE to have your husband back you on this, since it's his mom He has to control this, not you (I talked to her until I was blue in the face, it made no difference). You need to talk to him and let him know how much this is affecting you, if you need to talk let me know, i'll be happy to give you my email or phone number. I sooo get what you're going through.
Also, to the people below judging, that is not fair! With prices the way they are nowadays it is just not possible to pay upwards of $2,000 a month for daycare in addition to mortgage/rent, food, etc.. sometimes you just have to bite the bullet and fight your battles. However, I do believe this is one that needs to be fought. Just don't judge her for trusting her most precious gift, her son, to family. This is not he worst thing in the world, naps will be taken when he's tired enough. . atleast he's being well taken care of.
It will all get better. . in time.
Good luck!