Help..my 19 month old won’t sleep

Michelle • Baby 💗 born 6/11/17 & 💗 born 8/27/19

Today my child didn’t take a nap...has been up for 15 hours straight and is refusing to go to bed. She’s exhausted, I’m exhausted. This has been the trend for the past 10 days. She used to be a pretty good sleeper. Help!!! 😭😭😭