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As to the first part of your question: Because airlines are required (under their agreements with the countries into which they fly) to return to the point of departure at the airline's expense travelers who are refused admittance at their destination, air carriers are scrupulous to check passenger admissibility before allowing them to board the flight.
Airlines use the IATA database of TIMATIC for this purpose. TIMATIC will advise (correctly) that a Venezuelan national requires a visa to enter the UK. As @phoog points out in the comment below, there's an exception for holders of a carta di soggiorno di familiare di cittadino dell'Unione; with that card, and if she is traveling with or going to join her husband in the UK, she'll be allowed to fly. If, however, she holds only a permesso di soggiorno, she will not be permitted to board the Milan > UK flight.
As to the second part of your question: If your wife can get to the UK border without flying (say, by taking a train to Paris and presenting herself at the juxtaposed UK immigration controls at Eurostar in Paris), she can present the packet of documents you list to UK immigration as she attempts to board the Eurostar to London. As with flying, if she holds a carta she should be allowed to travel to the UK. If she does not, I do not know if the remaining documents will assure her entry to the UK.
If she were refused, or you decide to delay your return to the UK to avoid the uncertainty, you'll have to wait to secure a visa when consular offices and their contractors begin work again.