MIL wants baby to 'cry it out'

my MIL always criticises us for not just letting our 9 WEEK OLD(!!!) cry it out because we're creating habits and that it's a bad thing that he knows we'll tend to him anytime he cries. he's literally 2 months old?? he barely knows who his dad is, does she really think he understands?? she's even said that when she looks after him she'll just let him cry because she's 'his nanny and she doesn't have to do what mum and dad say'. like?? congrats now you've just dug yourself a hole because you won't be looking after him until you wise up. he's going through a sleep regression and she thinks it's appropriate to not comfort him when he's tired? like i said he's 9 weeks old, he doesn't understand 'cry it out', if we ignore him he doesn't understand that we're still in the room with him. she says that she did it with all of her kids and gave them tough love while they were getting older. meanwhile all of her kids constantly have problems with her?? im actually trying to build a good relationship with my baby. it also quite frankly upsets me to hear him cry, even when i know nothing is physically wrong.