I don't feel at all surprised about this. I have a girl,who is now 19 months old. She behaved in this same way. She was happy when she is in my house but keep crying when she is in my husbands place. In our place its a custom that the mother and the baby,after delivery,stays at the mom's place for atleast for first 28 days.
I think she cried, because, she didn't feel comfortable at my in laws place. At my place, my mom n my dad, where too exited to have their first grand daughter,that they hardly leave her alone, always use to play with her. And moreover i am also very comfortable at my place. But this is entirely opposite in my in laws place. In my in laws place, i have work to do n upon that don't have time to sit with my baby n play, in fact i don't feel comfortable there. Its not that my MIL is bad, but its just that she is too interfering one, so i feel a little uncomfortable. And i have read somewhere that the babies can understand their mom's mood.
Are u comfortable at your in laws place? If not, then may be your baby is crying because of that.
Hopefully i don't stay at my in laws place. Me n my husband stay in another house. But my mom in law came here for a visit for 3 months. And since this is the first time after our marriage, that m having time alone with my MIL, So now we understood each other n i do feel comfortable with her, so do my daughter now.
Try leaving your baby to spend time with your in laws, let her get comfortable there herself. I am sure, she'll get adjusted to your in laws.