Cry wolf
Definition 1 of 1
Pro Tip 1/3Overuse Risks
Using 'cry wolf' too often may lead others to doubt your sincerity, even in real emergencies. 
After Jack cried wolf several times, his friends ignored his calls for help.
Pro Tip 2/3Idiomatic Origins
The phrase originates from Aesop's fable, where a shepherd falsely claims a wolf is attacking his flock. 
Like the boy who cried wolf, she was ignored when the crisis was real.
Pro Tip 3/3False Alarms
'Cry wolf' suggests deception or joke, not just mistake or misunderstanding about danger. 
She cried wolf about the project deadline, but it wasn't actually due until next week.