Sounds like she will need to stay in Luanda on such a short trip, which is a shame, as there are some great sights a few hours outside the city! Fortaleza de São Miguel and associated museum is interesting, as is the Mausoleum of Agostinho Neto space needle thingy. Plus you can checkout the Angolasaurus at the Museum of Natural History! If you're feeling more adventurous (and the weather is good) get a boat over to Mussulo and go to Bar Ssulo or one of the other beach bars on the peninsula.
For restaurant recommendations check out
https://lnl.co.ao/
Agree with
cargueiro that changing on the street is not a good idea without some experience, but the difference in official vs street rates right now makes it very tempting (today 1USD = 465 Kwanzas official but 690 street rate!)