How should we sneak out?

me and my friend had 2 guys over last week while her parents were in ireland.when her grandma came home to check on her,only one guy had time to get out the back door and the other had to hide.but her grandma saw his refletion in the window.we didnt know we got caught till after he parents got home.her mom wasnt mad she was all like i was ur age once blahh blahh blahh but she did say if it happens againim not aloud over ever again.i'm sleeping over her house tomorrow night and we wanna sneak out to meet the two guys cuz we live like 15 min walkin distamce from eachother and our middle school is right in the midle so we could meet there.but im afraid that after what happened her mom will check on us during the night and we'll get caught even tho she has snuck out a million times before.it will be my first time EVER DOING IT.what should we do?