I don't know what the percentage of the final grade is but the pass level is 50% - so you need to get 25 out of 50 questions right to pass. The test is 1.5 hours covering units 221,222,223,228,229. (Assuming it is the revised Level 2 - old Level 2 may be different)
Your mum should be able to ask for help with the computer aspects before the exam - my college has offered help to anyone not familiar with computers - she must ask for help if she is worried about it!
There is no online practice system , but again college have offered to give us old papers to revise (bearing in mind these will be the old Level 2 so some bits are not relevant)
Good luck!