This all sounds very odd.
I think perhaps you misunderstood the payment schedule and assumed that her willingness to wait for the first month meant she would wait every subsequent month. If you are indeed paying two weeks late every month, then I can understand why she is chasing you. I'm not sure why you didn't clarify this when she first raised the issue. She should not have to chase for payment. She has bills to pay and, if she's going overdrawn each month, that explains her annoyance.
There is nothing wrong with her taking children to another childminder's house. We often do this. It helps the children to socialise and play with different toys and activities. Would you be worried if she took your son to playgroup, or on an outing? Another childminder's house is no different: it's a registered, inspected setting.
Nor is it really an issue if she has friends or family to visit, so long as they are not left alone with the children and DBS checked if they're regular visitors.
If you are not happy with this, then think carefully about using a nursery.
Some have visiting parents in, host drag story time, or even take children to inter-generation playgroups at care homes with few checks done as to suitability of premises or residents and staff. You would need to check and make sure you are happy with any such arrangements.
I suspect the reason why she kept sending your child home while you had Covid is that she was worried about infection. I'm seeing a lot of concerned posts on SM from childminders expected to take in children with positive cases at home, sometimes the children themselves have symptoms.
Biting is an issue for all Early Years settings, as you'll see if you look on the nursery page.
Screaming at you down the phone is really bizarre! I'm at a loss to understand why you've continued to send your child into the care of someone who sounds so unbalanced.
That's the problem with refusing to pay her notice, you see. You haven't immediately removed your child from her care following any these incidents.
By continuing to send him, it looks as though these issues weren't really as bad as you're now saying. It looks as though you're finding reasons to avoid paying the notice period now that you've found an alternative - this is a very common tactic that nearly every childminder experiences at one time or another. The other is to threaten to report to Ofsted, and that's why Ofsted will not get involved if there is a contract dispute.