I had a good friend (well acquaintance really - we were on a course together but are friends on FB) who is an Irish traveller.
She's lovely and her family is quite respectable.
However, her daughter's were chaperoned to the cinema until they got engaged. If they were not chaperoned, it was seen/thought among the community that she was tainted. They all got engaged (I think she has 3 daughters at age 17 approx.)
While living within the community, these things have weight, trying to live in a settled community, with a non-traveller mother is going to be tough.
You haven't lived the life, nor can you appreciate the reasoning behind their unusual views on things.
Would your partner be willing to let your dd be brought up in the contemporary environment she lives in?
It's different when you're part of a community, but you are not, nor is your dd.
And I also agree with a previous poster, that they really do dress like they're on a night out, just going to Mass even.
I have nothing against travellers. But knowing them, they are quite different in their mindsets. You'll be like rebels without a cause, without the back-up of a wider community.
I would think hard about this, as it's not choosing one community or another - it's choosing to rear your child under principles that she won't be seeing anywhere.
And to the poster who asked 'traveller' is recognised as an ethnicity in Ireland and thus protected, but I don't know about the UK.