Does she know the individual sounds that she should have been taught by now? Concentrate on single sounds at first; at least if she knows those, she is on track for the next stage.
If you can, cover pictures so she isn't looking for 'clues'. And don't just tell her the answer, but put the onus back on her by asking her another question: so in your example, when she says 'rucksack', ask her what is the first sound she can hear in 'rucksack', and exaggerate the 'rrrrr' sound (not easy to do maybe, unless you are Scottish!)
If she has a white board and pen, or paper and felt-tip, see if she can shape the letters; or do them on a shallow tray of sand or flour.
Reading is a very advanced concept and skill, and if she is only five, it is little more than two or three years since she first learnt to TALK - so she has come a very long way!
If you want to do more with her, there is a very useful book for all the family:
An inexpensive and easy to use book, that can encourage children with reading, spelling and writing, and really help them to understand Phonics, is reviewed in the MN Book Reviews section. Just search ‘Phonics’ and my name.