100%, I dont understand how she managed to let her poop on her mums bedroom floor when they were literally in a bathroom. Over the toilet, hell, just hold her in the bath til she was done cos there was a mess to clean in there already
Mabel is not necessarily too young to be potty trained (I know many, including myself and siblings, who were fully potty trained under 2) but it depends on the child and their ability to communicate and acknowledge it. We don't hear Mabel say many words or communicate with that many hand motions tho so she probably isn't ready as of yet.
If Mia has another baby when she wants then I dont see Mabel being potty trained until she's much older especially because I doubt Mia has the resilience to keep up with potty training a toddler whilst looking after a baby/another toddler.