Dear Aoife, I just came back from CP, Porto to Santiago. I did not do it alone, however I passed by many women walking solo.
The trail is very safe and people are lovely (even more than in the CF, I thought!). I also think very comfortable walking shoes are a good choice. There is a fair bit of stones, paved roads and asphalts, so cushioning and softness, at least for me, were more important than firmness of ankles or anything else.
I cant say anything about the trail between Lisbon and Porto, but you will probably have a great experience. Do not miss the opportunity of eating "natas" (Portuguese custards). Even if you are not a fan of custards, try them - they are a local pride and absolutely delicious!