Agreed, Retro, it ain't rocket science. And I find it a pity that others advise not to do it just because they don't want or haven't tried. The LR has become a lot more user friendly over the last ten years.
You are going to need this TR1 form as it is the whole of the registered title: -
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/390836/TR1__web_friendly_PDF_.pdf
There are various accompanying notes to help that can be downloaded separately.
I think there is a requirement to pay Stamp Duty Land Tax on the transaction, I'm afraid, in respect of the two-thirds assessed value sum being paid by your sister (the figure that will appear as the Consideration in Box 8 of the form). That is going to cost her, depending on the value of the property. There is a separate form for this. Not 100% sure on this point, others may wish to correct.
If you go to a conveyancer or solicitor, legally they will have to follow a minimum process of due diligence, else they could be later accused of not advising client properly. As a minimum this is going to mean an assessment of the title for defects, and probably a local search.
Your sister needs to understand that she is acquiring the property 'as seen', but if it has been in the family for a good number of years, the family know as much about it as it likely to be important.
Both solicitors and conveyancers assess how much they will charge based on the property transaction value, with conveyancers charging roughly two-thirds of what solicitors charge for the same thing. So none of us can answer your actual question (because we don't know). Phone a few for a quote - they do that over the phone.