jemanden im Stich lassen
To abandon a person who was counting on you.
jemanden hängen lassen
To leave someone hanging. One fails to deliver what the other person was relying on.
jemanden im Regen stehen lassen
To leave someone standing in the rain. One withholds help that the other person expected.
jemanden versetzen
To stand someone up. One does not come to an agreed meeting.
Auf sie ist Verlass.
She can be relied on.