She now has started saying how hard I am going to find the first few months and that I “will need my mum” as another way to get me to allow her to visit.
Hmmmmm. In my experience, the kind of people who will try and steamroller, manipulate and guilt you into doing things the way they want them are EXACTLY the kind of people to avoid when you have a newborn. If it's your mum who is all set to be Granny MeMeMe then that goes double.
You will need space, peace, and people who are willing to quietly support you while YOU get the hang of things and get to know your baby. You will very much not need someone intent on pushing her needs into your face too. It's a sure-fire way to get stressed, and fall out, and that would be a shame.
I just don’t like feeling like I’m not being taken seriously.
You will like that even less when you have the responsibility of a newborn, and you're actually doing fine, and she's pushing her own agenda.
I think her insinuating that I won’t be able to cope with a newborn pushed me over the edge
And that's where you draw the line - really, or as I said above - you will fall out. And that's the last thing either of you need, really, especially as she is bereaved.
Use this to your advantage. Be firm, mainly to let her know that no, you won't be pushed around regarding the baby - you'll be mum, what you say will go. Definitely use the 'wait and see' line - and make it clear that regardless, what you will need is uncritical support, and a lot of peace and quiet, a lot of time just with the baby, and that wouldn't change with no lockdown. Shut down any crap about you not coping - 'Mum, I'm sure that didn't come out as you meant it. If you're going to start undermining me by suggesting that I won't cope with my own baby then no, you'd be the last person I'd want around me. Don't say things like that, I don't want us to be on bad terms.'