I sell vintage and antique pottery - it's not true that all of it is worthless, and indeed the poster saying that Americans buy Victorian stuff but are unreachable, yes they do buy and I post it by Royal Mail absolutely fine.
Of course the value for some stuff has decreased a lot, but it's stil worth selling surely if it brings you a couple of hundred.
Some specific things can sell very well - including COSTUME jewellery, let alone fine jewellery - it depends whether she's got anything trendy.
Auction valuations are best because they don't need a mark-up for themselves, but they would usually value at a minimum. Some would sell for more, some wouldn't sell at all - they can try again a couple of times if not sold.
Cheap/trinket stuff can still sell if you put them into a big group, OP- not logical, but they just do. People buy these to sell at car boots (though not sure when they will open - only summer probably). Again auction group things like these, but be aware that people do steal from boxes during auction previews - when viewings are allowed.
You could send me a photo of ceramics etc if you like, OP, to give you an idea if these would currently sell or best to take to charity shops, if you want several opinions.