Solo female travelers visit Egypt regularly, and organized tours and Nile cruises in particular remove a lot of the usual solo-travel friction, since transport, guides, and daily plans are already arranged rather than negotiated on the spot.
Dress and everyday interactions
Dress modestly, especially in rural areas, mosques, and souqs, is standard travel-advisory guidance for Egypt as a whole — covering shoulders and knees tends to reduce unwanted attention and is simply expected at religious sites regardless of gender. Confident, direct responses to unwanted attention from vendors or touts are generally effective and normal here.
Sticking to licensed transport, staying in well-reviewed accommodation, and keeping someone updated on your itinerary are sensible general practices that apply as much in Egypt as anywhere else — see What Common Tourist Scams Should You Watch For in Egypt? for the specific patterns worth knowing.