It doesn't have to cost the earth. I've got back to 1600 on the line I really wanted to research and I've only ever paid for a Genes re-united account. Having an unusual surname helps, I found a distant relative who'd spent years doing all the hard work for me... I still have to trace the family lines which have ridiculously common surnames, but even there I've got back quite a way without paying anything.
The Church of Latterday Saints do a fantastic free to download program Called Personal Ancestry File (PAF)for recording all your info. They also have lots of records on their site.
www.familysearch.org/
The storage on Genes-reunited is good, but PAF is much more thorough and much quicker.
FreeBMD also has lot of Birth Marriage and Death indexes, so if you've got a vague idea of what you're looking for you can usually work it out without needing to buy the certificates.
www.freebmd.org.uk/
There's also FreeCen
www.freecen.org.uk/
Both FreeBMD and FreeCen are ongoing transcription projects being done by volunteers, so they're worth rechecking every few months as new names are constantly being added.
Someone has already mentioned Rootsweb, and there are also area or name specific mailing lists where you can ask for lookups, and may find relatives too.
The most useful thing she can do is talk to relatives, then when she gets bits of information talk to them again, a new name might jog their memory. Also ask them if they have any old documents. My search started when I found a suitcase full of very old certificates, documents and photos at my Grandparents house.
I was interested when I was a kid, but I was too young to really make much sense of what people told me, and there weren't all these free resources back then. I wish I could quiz my Grandparents now, although I'm not sure they'd talk to me, I've found too many skeletons
My top tip for her is to make a note of exactly where she finds out any information (PAF allows you to add source information). That way she knows if it's from a certificate, so absolutely definitely correct, or whether it's from someone on Genes-Reunited, so could be completely made up, it happens a lot. I tend to spend a week researching, then leave it for a few months. If she does get bored with it she'll be able to come back to it in a few years and know how accurate her information is.
Good luck to her, it's great fun, but very addictive