Izhevsk, is relatively safe for solo female travelers. During the day, the city's main areas are bustling and well populated, so you are unlikely to encounter any sort of trouble. As in any location, common safety rules apply such as not wandering off to deserted places alone, especially at night. However, knowing some basic Russian words would be extremely helpful since not everyone speaks English. If you stay in touristy areas, take normal precautions as you would do in any urban area, your trip should be worry-free.