You don’t sound difficult to me, your mum is probably hurting but that doesn’t mean it’s your fault.
I a have similar issue, my mum used to look after my DD on a regular basis and when the first lockdown hit that stopped, and she hasn’t looked after her now in over a year, although we do do lots of FaceTime and phone calls. I am hopeful that with easing of lockdown this will change however have been firm with my decision. It’s hard because I know my partner and mum would probably carry on as they were, technically breaking guidelines, as I don’t need the childcare as such and neither of us are from single adult households. My mum was also a bit loose with her ‘support bubble’ with another who was in single adult household but had 3 support bubbles. So I feel like I’m the cause of their upset. But I need to tell myself I am not, and so do you. I have a lot of anxiety around covid, mainly contributing to the spread than getting it myself, my mum works in a public facing role and she lives with my sister who works somewhere similar, my DD also goes to nursery.
I don’t get the snide comments, I’m sorry you are going through that, but I have been constantly asked for them to see DD or can they hug during the times when we were allowed socially distanced visits, when I’d already discussed what I was and was not happy with beforehand. This would upset me and cause me to feel so guilty, but actually I wasn’t asking them to do anything above what guidelines stated (UK). They are also aware of my anxieties and the guilt I would feel deliberately and unnecessarily going against guidelines.
I suggest being honest with your mum about how her comments are making you feel, that they aren’t going to change anything you have decided, you’re not doing anything out of malice so the comments she is making are not helping anyone, only causing you further upset in an already shit situation. I also said to my mum I am equally distraught over the situation and agree it’s crap.