Hi I’m new here need some advice. I wrote before but no one replied

. Basically I know a person who came into this country on a visit visa she was 14 when she came around 2004 she has overstayed ever since. She came with a 5 other siblings they have all overstayed And married British citizens. She is now 27 I believe and has met someone who is a British citizen. Now my question is what is the best route for her to be legalised. I know her siblings got discretionary leave which is along process and is not always guaranteed. A lot of people say if she returns to her country then her partner can apply for spouse visa and that is a better option. My question is if she returns home would they ban her??? Considering she was only a child when she came here and overstayed. And how long before She can come back and how long will the spouse visa take to process. Any help will be much appreciated.