To expand on the previous post - you are indeed between a rock and a hard place.
If you wish to marry in this country, you should read the advice on the BIA website:-
http://www.ind.homeoffice.gov.uk/applyi ... artnership
with particular attention to Paras 3.2 and 3.8, and the warning in the latter that the Home Office will consider enforcement action against someone illegally here.
If they do that, it follows that getting a visa to return as a spouse could be very difficult.
If the lady succeeded in returning to Brazil without being served with a notice as an offender, she
might have a better chance of being issued with a visa, although to make a credible application would probably require declaration of the overstay. However, there is anecdotal evidence that ECOs are taking a harder line in such cases.
A further problem is that there are now checks at some embarkation points, where offenders could be held up. Certainly when I flew out of Heathrow a month ago there was a check - how extensive these are remains to be seen, but it is also possible that your lady could board her plane clutching a notice that she has "remained beyond the period limited by her leave".