You can usually buy certain brands that come with an international warranty (IW), or purchase a separate IW. With Dell one can easily transfer the warranty - e.g. when the owner moves from one country to another click here. I guess the same would apply when she moves back.
A laptop is a laptop in any part of the world, with the main incompatibility issue arising due to differing mains power arrangements between some countries & continents. This is usually easily solved by purchasing the right power adapters to use in each country.
Well, when shipping anything of high value (anything >£36 I think), you need to also think about:
1. The enhanced shipping costs to cover insurance
2. Import VAT (or similar)
3. Excise Duty to import it into the country.
A few related & useful links to look through at the HMRC website:
'Tax when ordering or sending goods from abroad' click here
'A guide for international post users' click here
You can also call & speak to a human being if you get stuck or need more specifics: "If you need more information about customs procedures for goods posted to the UK, you can contact the VAT, Customs and Excise Helpline on Tel 0845 010 9000. Lines are open from 8.00 am to 8.00 pm, Monday to Friday except bank holidays."
I'm sure the Forum Editor will know a thing or ten about this, being the avid traveller that he is :-). G