Minimum time between trips from USA?

Hi wanted to ask about this, wasnt sure where best to put it...

My girlfriend is American & has visited me in England from USA 4 times over the last couple years on a Visa waiver. She generally stays for about 5 months & goes back home for a similar period of time.

This last time she stayed there for 9 months & only visited here for 3 as she had to go back for her sisters graduation. Now she wants to come back over here & id love to have her here again but she's only been at home for a month since she left. How long should we wait before shes likely to be allowed back into UK? Is there a minimum time period? Would she be able to stay for the remaining 3 months she didnt use of the waiver time period?

Thankyou for any help offered ! Dont know if this is the easiest question to answer, just looking for advice & peoples thoughts/experiences really thanks !

Jonathan

There's no minimum period, so there is no problem with her coming back.

The only rules/guidance are that visitors should normally spend less than 6 months in the UK within a 12 month period and no visit should be more than 6 months.