It makes sense for her to go and discuss with a solicitor indepth first of all. Until he or she is in possession of the full facts he cannot really give a realistic estimate.
As JtH says, it really depends on the type of case because there are an awful lot of variables. The type of case it is will also impact on the likely costs rules (they differ from case to case). If her case is that good, she might be able to get the other side's case struck out.
£30k might be realistic. It might not. It may also be worth her checking her house insurance to see if she has any legal expenses cover. Also seeing whether she could do this on a no win no fee.
It is IMPOSSIBLE to say until a lawyer has seen the papers and reviewed the evidence and even then the best they can do is estimate.