Being a female tourist in Italy during the summer poses too many "what shall I wear" dilemmas.
There is a lot of walking to be done. This probably requires comfortable sandals but I reckon you can get away with flip flops at a push. There are also plenty of torre and duomo climbing opportunities. This is where sandals win against flip flops. One could consider trainers or similar but on a hot day that doesn't appeal.
Hot weather usually encourages Brits to dispense with as much clothing as possible. Women often wear strappy tops with very short shorts. This is a problem when trying to visit duomos. Italians, unsurprisingly, take religion very seriously and you must be dressed appropriately to be allowed entry into most churches or cathedrals. I've seen signs banning hats, strappy tops and short shorts or skirts. I think shorts that aren't very short are OK and a t-shirt with short sleeves is OK. I often wear sleeveless but not strappy tops and make sure I have a sarong with me to cover my shoulders and thus avoid causing offence.
I remember traveling with my friend Pam, Interrailing around Europe, in my early twenties. Either the Italians have become more tolerant of tourist dress (or lack of it) or I wear more these days.
Either way, nowadays, you are less likely to be refused entry for a lack of apparel. Attractions want your tourist Euros and will offer you a modesty cape made of paper if you aren't deemed to be wearing enough.