Yes, you will be able catch her in LSH in future update of that game.
No you catch Wendy in the tutorial, Mandy attacks you after you catch Wendy. I think lags is saying that in the future in the original LSH, we will be able to catch Mandy as well. I bet it'll have something to do with Wendy's questline that am totally assuming will eventually come (🤞🏻). When the original game gets worked on after this one and HTA.