Can you ask that girl if she is hot?

Of course. Asking whether one person feels hot is a common way to care about another person's comfort, especially in hot weather or high ambient temperature. Of course, you can ask girls if they are spicy, but it should be noted that you should respect each other's privacy and boundaries when asking questions. If you have a close relationship with this girl, or have established a good communication foundation, then you can politely ask her if she feels hot and take corresponding actions according to your feelings.