She was drowning in herself.

[shootingstar]

. . . , her phone vibrated in her hand.
. . .
'Oh hi, Doreen.'
An agitated voice. 'Where were you?'
She'd totally forgotten. What time is it?
'I've had a really crap day. I'm so sorry.'
'We waited outside your flat for an hour.'
'I can still do Leo's lesson when I get back. I'll be be five minutes.'
'Too late. He's with his dad now for three days.'
'Oh, Im sorry. I'M so sorry.'
She was a waterfall of apologies. She was drowning in herself.
'To be honest, Nora, he's been thinking about giving up altogether.'
. . .

(The Midnight Library by Matt Haig, episode Antimatter)

Does "She was drowning in herself" mean "She was drowning herself in a waterfall of apologies" in this context or is "in" preposition of "herself" there?

 

[tedmc]

It is an extension of the waterfall metaphor, i.e. she was drowning in a waterfall of her own apologies.

 

[jutfrank]

She was the waterfall. That's the metaphor. Therefore, she's drowning in herself.