Thanks for your question.
Romania is an EEA member state. This means that citizens of Romania holding Romanian passports therefore have free movement within the European Economic Area, this includes the UK:-
This means that if she is Romanian then she would not have had to have applied for a visa in order to travel here. She can just come here without restriction. She would only be denied entry if the official thought she was coming to commit a crime of some sort.
A ‘short' visit is defined as being less than 90 days, but the practical reality is that even if they note the extended stay leaving the UK she will simply be able to explain that it was an honest mistake on her part. It has to be something VERY serious for the UKBA to attempt to revoke someone's treaty rights and, quite frankly, they have more important things to do
This will remain the case in the future. She will not receive a ban when she leaves the UK because of her above mentioned treaty rights to free movement.
The situation applies to you travelling to Romania, they are an EEA member state and you can exercise your treaty right of free movement to travel there without applying for a visa. It's the point of having a European community really. If you are planning on visiting Romania for greater than 90 days in any one visit then you should contact the Romanian embassy to see if there is some kind of administrative procedure to go through, but it will be purely administrative - nothing like applying for a visa
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