Thank you for your question. I can certainly appreciate why you are concerned and the reason for your question. Yes, it could be potentially harmful to your child's emotional health for her to be separated from you and your husband for this extended amount of time. Notwithstanding that your mother-in-law has had limited contact with her, your daughter is too young to be away from her primary caregivers.
One of the concern that is related to her limited contact with her grandmother but also a developmental issue is separation anxiety. This type of anxiety starts between 6 and 8 months but separation anxiety may take until age 2 to 3 years to finally peter out. As in much of infant development, the child's temperament plays a role. A child who adapts to new situations easily will probably have less anxiety than the child who has a difficult time with change. Because she does not have regular contact with your mother-in-law it would be normal for her to have some apprehension and trust issues in general.
Again, regardless of her temperament, I think its too much time for any 2 year old to spend an extended amount of time away from their parents despite how strong or weak the connection to the person. I think its important that some arrangement be made for more consistent contact to allow for such a trip in the future. If she cannot physically visit often, frequent phone calls, pictures in your home that are visible and that your refer to (for example, where is grandmom? so she can start making the connection and identifying her and a loving person in the family), she can send letters to your daughter and you can sit together and read the letters. The association that her grandmother loves her and thinks about her will assist with building a bond.
I hope this information is helpful. Good luck with making the decision and I hope your mother-in-law understands that your intention is to protect your daughter's emotional well being and the choice is unrelated to her ability to care for your daughter or that you do not support a close relationship between them.