Yeah it can be really hard. I had a tricky phone call today with DH's cousin, looking for some bf advice, and she made a comment about someone saying her 4mth was "manipulating" her because she cried so cousin picked her up, apparently she's now manipulated her into knowing that if she cries she will get picked up. I got so mad, I was like "Hun she's 4mths old, she has needs and wants. She needs to be fed, clean bum, warm and safe. She wants to be with you. It's as simple as that."

So... Here's an ABA article on sleep, which mentions control crying: https://www.breastfeeding.asn.au/bf-info/sleep/wakeful

Also you could google Pinky, she has some articles on there, can't link here though.

Or - consider buying her the No Cry Sleep Solution, as a gift and presenting it to her as an alternative to Dizzie.