Umm no actually she lives abroad and visits the UK occasionally.
Yes it happens that people reach the survey from around the world ^_^!
To overcome this you could either put the eligibility criteria at the very beginning of your survey so that people who are not eligible (e.g if outside the UK) won't be able continue OR have a question on country of residence as part of your demographics section, this will help you in analysis to add a filter to exclude responses from outside the UK.
On another note, I think the context (country) can be a potential confounding factor in your study. Because cultural factors and ethnicity might have an influence on perceptions, in addition to the availability of the brand (H&M) in some countries compared to others.
For an MSc dissertation this should be fine, and any challenge or missing point can always be discussed in the discussion/limitations/reflections section in your final thesis.
I'm sorry, this is just from a methodological point of view, you are an expert in this more than me