Jamie Lynn Spears gave us a peek into her upset over her relationship with her big sister, Britney.

Jamie Lynn posted what sounds like tearful audio ... 3-year-old daughter Ivey is heard saying, "It'll be okay, mom, it has to be okay, mom." Jamie Lynn sounds like she's fighting back tears, as she says, "Thank you, baby."

The audio, recorded Saturday night, underscores the drama in the Spears family. Britney has made it clear ... she believes her mom, dad and sister have all betrayed her over the conservatorship. Britney says they've all profited from it, at her great expense.

Britney posted last month, "Never forget who ignored you when you needed them and who helped you before you even had to ask."

To show the depths of the conflict, Britney added, "How dare the people you love the most say anything at all … did they even put a hand out to even lift me up at the TIME !!!??? How dare you make it public that NOW you CARE … did you put your hand out when I was drowning????"