There are some herbal remedies to aid sleep available from health shops, herbalists and pharmacies but I suggest you cut all caffeine from your diet and drink something that aids relaxation like camomile tea and make sure you have a later supper with plenty of green salad.
Being in the right frame of mind for sleep is important so something like a ten minute stroll (without pressure and with an empty head) in the fresh air could be valuable...
The reason you are not sleeping probably has as much to do with your state of mind than with the noise your sister is making - few people sleep or rest properly when they are uptight because they are irritated or because the brain is buzzing...
You can try any of the relaxation techniques based on self-hypnosis but what worked for me is laying on my left side and replaying the day on my mind's eye, sorting out things in my head and then turning on to my right side with a relatively empty mind meant I couldn't stay awake if I wanted to...
Failing all that you could try making your sister wear her computer like a necklace or arrange for the power to be cut off...
Would it be possible to borrow a bicycle which would save you more than two hours each day and cost little more than walking. Failing being able to borrow a bike such things are sometimes given away and in some parts of the world serviceable cycles can found in scrapyards and landfill sites.
Perhaps your sister would place a request on your local freecycle, or similar site?
Good luck with your course...