Mei likes to be tied up for fun, so she makes for some good snuggling. However, that's also a good time for her to enchant her captor with her moe appeal. Even if she's gagged, all it takes is one potential "onii-chan" for her to turn the tables. But if she's captured by someone she doesn't like, she will easily get scared and people will come looking for her. She knows how to use her cuteness to advantage in either case, but it's far better for everyone if she's on the captor's side. Give her a cute gag to compliment her face.