Oh mama, you're definitely not a lousy mum, this is so common in the first month or two, honestly. Your baby's probably picked up on the nanny's calm confidence and routine, and that doesn't mean you can't get there too. A few mums I know found it really helped to shift the nanny into more of a coaching role rather than taking over completely, like, ask her to guide you through a feed or a nappy change instead of just watching her do it all. That way your baby gets used to you doing it, and you build your own rhythm without the pressure of figuring everything out solo.
The other thing that made a difference for people around me was actually doing the night feeds or the early morning routine yourself, especially if the nanny sleeps then, breastfeeding in particular is such a strong bonding tool, and it gives you that one-on-one time to get comfortable with your baby's cues. Sometimes babies cry because they're still learning too, not because you're doing it wrong.
Since she's been with you over a month now, maybe have a chat with your nanny about gradually stepping back in certain areas before she leaves? That way it's a smooth handover rather than a sudden shift. And do check in with your doctor or a lactation consultant if the crying feels really distressing, they can also rule out anything like reflux that might be making baby unsettled in general.
You've got this. It really does get easier.
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