She will probably be allowed reference only access through SCONUL, or some will allow anyone a limited number of non-member visits, e.g. Where I was at uni you could go in 10 times a year as a non-member.
As far as I know there is a reciprocal arrangement between UK university libraries. See this site to check if this applies to the library she's hoping to use: http://www.sconul.ac.uk/sconul-access. Note she'll need various forms of ID and check opening hours. Note also that most university catalogues are available online; she may be able to gain access to her own university's journal subscriptions via the Internet (assuming of course she's not in need of good old fashioned books!).