Just verifying re friend visiting UK for a few months

Ok. I am completely and totally out of the expat loop. I haven't checked new immigration stuff in ages. So here's my stupid question :

A friend of mine is coming from US to visit DH & I next month. She is hoping to stay for a few months, but no more than 5 or 6 at the most. The last information I heard was that she could stay up to 6 months - is that still correct? She's not planning on working or anything like that. She is currently in the process of a medical retirement from her job, so hasn't been working in over a year while on long term disability. Her illness is exacerbated by stress, and she has had a really tough time of it. We're hoping that instead of being home alone and stressed (especially over the holidays), that coming over here, getting out and about, and being around friends, will be a tremendous recharge for her and allow her to enjoy herself for awhile. She will not need any ongoing medical treatment, just takes meds which she will get regularly shipped over here while she's visiting. No plans to overstay or trying to work or anything. Just an extended holiday to destress and allow her time to recuperate some.

Any thoughts on any potential problems? She does plan on making sure she has the return flight booked, so she has a return flight with a definite date on it for when she goes through immigration - with a date just short of 6 months. She's never been to the UK before and is really looking forward to this. I just want to alleviate any possible stress for her. I'm assuming still no visa required for this type of visit, right?
Thanks.

A stay of that long will always raise eyebrows.  She should have an invitation letter from you as well as evidence that she can support herself.  Given the circumstances, I think a letter from her doctor may help as well.

Vicky

Vicky - thanks so much! I didn't even think of that. What would be good evidence that she can support herself - bank account info for the last couple months showing regular monies going into her account?  And when you say letter of invitation - do you mean a letter written to HER or one written specifically for purpose of questions from immigration (such as "I have invited her to stay with us for this amount of time - she will be living with us, etc etc"). I'll mention to her the doctor's letter, as I'm sure he would write one. He's been telling her for months she needed to take a break and give herself time to get better.

Either letter will do, and yes, bank statements.

Vicky

Great - thanks.

You can also write it directly to the duty IO. 

The advantage in that approach is you do not have to use the 'broken eyeline' style and therefore the letter is more genuine.

Alright. Thought I was done with stupid questions, but apparently not. What is "broken eyeline"??

Also, if I do the letter directly to IO, do I include a brief history (such as the fact that we are longtime friends from working for a number of years together in the police department, that she is staying for an extended period with us - just under 6 months, plus she's never been to England so wants to do a lot of the tourist stuff over that time period as well) so that they have that type of info?