Reimu didn't notice the glass box had an open top.
Even if she had, she might not have been able to jump high enough to get out, or might have been under threat of having her children killed horribly (too late!) if she escaped. Without a translation it's tough to know.
3:There's no lid on your case,so if you wanted to get outyou could do so on your own.
Rather...Didn't you notice it was open above you?Are you stpuid?wanna die?
4:Did you think there was a mister clear glass above you?
Dumbass Reimu. She didn't even try to jump out of the case.