Nearly every post is setting out their lived experience.
This is mine ....
I am retired now but one of the jobs I held for 10 years involved me working very closely (and exclusively) with and alongside traveller communities of all kinds in England.
What I found is that travellers are much like you and I - some good, some exceptionally good, some bad, some exceptionally bad. Because their community is often more visible, the bad bits are more obvious and therefore bring down hatred on all travellers.
I deeply admired their family loyalty and respect for their history and traditions. I liked less their attitude to women's roles (though this is changing a great deal now and there are many well-educated travellers, both men and women), the times when they settle arguments with fists rather than negotiation, their unwillingness to integrate with the settled community, and the disrespect from SOME traveller groups for decent societal norms - like not leaving a mess for others to clear up..
Some of this is however understandable, given that in the recent past they have found themselves a beleaguered group since their previous traditional roles have been wiped off the map - e.g. seasonal agricultural work. And their former totally nomadic lifestyle can no longer prevail as there are few stopping places.
In the main travellers are the cleanest and tidiest of people - I have been welcomed into many trailers and they are spotless - you could eat off the floor - and they leave the plastic covers on the seats to keep them clean. These travellers are as appalled as you or I by the bad behaviour of a minority.
I have been to traveller fairs to interview people and take photos and they joined in with humour and good will.
Some whom I met I counted as friends; some I would be very happy not to meet again. But that goes for other human beings too.
I do not know what the answer is, but I also feel for the local authorities who have a legal duty to make provision for travellers in their area but get slagged off good and proper when they propose a site. Rock and a hard place for them.
On the topic of the OP's proposed house ..... in spite of my awareness of decent traveller communities and my inclination to stand up for them, this is such a huge purchase for her - a massive financial and life commitment - and if there is any chance that resale might be a problem then I think she has no choice but to withdraw from the purchase.