Does she just have a right of residence in the property or replacement (sounds likely) or a full life interest in the estate? Who has responsibility for paying the mortgage? Who are the trustees?
If she is being harassed like you say, it may be worth varying the trust (a trust bust). The beneficiaries can agree on what shares they wish, but the fairest way is to obtain an actuarial valuation to break the trust. However, if she is in her 70s, she will probably not get much. Although it will be a clean break.
Given that she has the right to require a replacement property, would she consider "downsizing"? Pay off the mortgage and give the remaindermen a few quid and give the life tenant a smaller property which she can manage on her own?
If it is any help, it is actually damn difficult to "prove" non residence. Your friend should take legal advice since there may well be other avenues open to her such as a claim under the Inheritance (Provision for Family and Dependants) Act 1975, if this is within 6 months of the grant of Probate.