15months old daughter clenching her leg

My 15-month-old has been clenching her legs together during diaper changes. I first noticed it about two months ago, but I didn’t think much of it. However, my mother-in-law just mentioned she observed the same and suggested I get it checked. My sister-in-law also brought it up two weeks ago and advised me to speak to the nursery, as she feels it’s not normal. She was not doing this before nursery. Now, I’m starting to feel concerned, especially since I’ve already been uncomfortable with different people changing her diaper at nursery. I’ve been meaning to bring it up, but I’m not sure how to approach the conversation. Any advice on how to handle this? P.S. I’m a first-time mom.